/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
/* Copyright (c) 2011-2014 PLUMgrid, http://plumgrid.com
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of version 2 of the GNU General Public
 * License as published by the Free Software Foundation.
 */
#ifndef __LINUX_BPF_H__
#define __LINUX_BPF_H__

#include <linux/types.h>
#include "bpf_common.h"

/* Extended instruction set based on top of classic BPF */

/* instruction classes */
#define BPF_JMP32 0x06 /* jmp mode in word width */
#define BPF_ALU64 0x07 /* alu mode in double word width */

/* ld/ldx fields */
#define BPF_DW 0x18 /* double word (64-bit) */
#define BPF_XADD 0xc0 /* exclusive add */

/* alu/jmp fields */
#define BPF_MOV 0xb0 /* mov reg to reg */
#define BPF_ARSH 0xc0 /* sign extending arithmetic shift right */

/* change endianness of a register */
#define BPF_END 0xd0 /* flags for endianness conversion: */
#define BPF_TO_LE 0x00 /* convert to little-endian */
#define BPF_TO_BE 0x08 /* convert to big-endian */
#define BPF_FROM_LE BPF_TO_LE
#define BPF_FROM_BE BPF_TO_BE

/* jmp encodings */
#define BPF_JNE 0x50 /* jump != */
#define BPF_JLT 0xa0 /* LT is unsigned, '<' */
#define BPF_JLE 0xb0 /* LE is unsigned, '<=' */
#define BPF_JSGT 0x60 /* SGT is signed '>', GT in x86 */
#define BPF_JSGE 0x70 /* SGE is signed '>=', GE in x86 */
#define BPF_JSLT 0xc0 /* SLT is signed, '<' */
#define BPF_JSLE 0xd0 /* SLE is signed, '<=' */
#define BPF_CALL 0x80 /* function call */
#define BPF_EXIT 0x90 /* function return */

/* Register numbers */
enum {
  BPF_REG_0 = 0,
  BPF_REG_1,
  BPF_REG_2,
  BPF_REG_3,
  BPF_REG_4,
  BPF_REG_5,
  BPF_REG_6,
  BPF_REG_7,
  BPF_REG_8,
  BPF_REG_9,
  BPF_REG_10,
  __MAX_BPF_REG,
};

/* BPF has 10 general purpose 64-bit registers and stack frame. */
#define MAX_BPF_REG __MAX_BPF_REG

struct bpf_insn {
  __u8 code; /* opcode */
  __u8 dst_reg : 4; /* dest register */
  __u8 src_reg : 4; /* source register */
  __s16 off; /* signed offset */
  __s32 imm; /* signed immediate constant */
};

/* Key of an a BPF_MAP_TYPE_LPM_TRIE entry */
struct bpf_lpm_trie_key {
  __u32 prefixlen; /* up to 32 for AF_INET, 128 for AF_INET6 */
  __u8 data[0]; /* Arbitrary size */
};

struct bpf_cgroup_storage_key {
  __u64 cgroup_inode_id; /* cgroup inode id */
  __u32 attach_type; /* program attach type */
};

/* BPF syscall commands, see bpf(2) man-page for details. */
enum bpf_cmd {
  BPF_MAP_CREATE,
  BPF_MAP_LOOKUP_ELEM,
  BPF_MAP_UPDATE_ELEM,
  BPF_MAP_DELETE_ELEM,
  BPF_MAP_GET_NEXT_KEY,
  BPF_PROG_LOAD,
  BPF_OBJ_PIN,
  BPF_OBJ_GET,
  BPF_PROG_ATTACH,
  BPF_PROG_DETACH,
  BPF_PROG_TEST_RUN,
  BPF_PROG_GET_NEXT_ID,
  BPF_MAP_GET_NEXT_ID,
  BPF_PROG_GET_FD_BY_ID,
  BPF_MAP_GET_FD_BY_ID,
  BPF_OBJ_GET_INFO_BY_FD,
  BPF_PROG_QUERY,
  BPF_RAW_TRACEPOINT_OPEN,
  BPF_BTF_LOAD,
  BPF_BTF_GET_FD_BY_ID,
  BPF_TASK_FD_QUERY,
  BPF_MAP_LOOKUP_AND_DELETE_ELEM,
  BPF_MAP_FREEZE,
  BPF_BTF_GET_NEXT_ID,
};

enum bpf_map_type {
  BPF_MAP_TYPE_UNSPEC,
  BPF_MAP_TYPE_HASH,
  BPF_MAP_TYPE_ARRAY,
  BPF_MAP_TYPE_PROG_ARRAY,
  BPF_MAP_TYPE_PERF_EVENT_ARRAY,
  BPF_MAP_TYPE_PERCPU_HASH,
  BPF_MAP_TYPE_PERCPU_ARRAY,
  BPF_MAP_TYPE_STACK_TRACE,
  BPF_MAP_TYPE_CGROUP_ARRAY,
  BPF_MAP_TYPE_LRU_HASH,
  BPF_MAP_TYPE_LRU_PERCPU_HASH,
  BPF_MAP_TYPE_LPM_TRIE,
  BPF_MAP_TYPE_ARRAY_OF_MAPS,
  BPF_MAP_TYPE_HASH_OF_MAPS,
  BPF_MAP_TYPE_DEVMAP,
  BPF_MAP_TYPE_SOCKMAP,
  BPF_MAP_TYPE_CPUMAP,
  BPF_MAP_TYPE_XSKMAP,
  BPF_MAP_TYPE_SOCKHASH,
  BPF_MAP_TYPE_CGROUP_STORAGE,
  BPF_MAP_TYPE_REUSEPORT_SOCKARRAY,
  BPF_MAP_TYPE_PERCPU_CGROUP_STORAGE,
  BPF_MAP_TYPE_QUEUE,
  BPF_MAP_TYPE_STACK,
  BPF_MAP_TYPE_SK_STORAGE,
  BPF_MAP_TYPE_DEVMAP_HASH,
};

/* Note that tracing related programs such as
 * BPF_PROG_TYPE_{KPROBE,TRACEPOINT,PERF_EVENT,RAW_TRACEPOINT}
 * are not subject to a stable API since kernel internal data
 * structures can change from release to release and may
 * therefore break existing tracing BPF programs. Tracing BPF
 * programs correspond to /a/ specific kernel which is to be
 * analyzed, and not /a/ specific kernel /and/ all future ones.
 */
enum bpf_prog_type {
  BPF_PROG_TYPE_UNSPEC,
  BPF_PROG_TYPE_SOCKET_FILTER,
  BPF_PROG_TYPE_KPROBE,
  BPF_PROG_TYPE_SCHED_CLS,
  BPF_PROG_TYPE_SCHED_ACT,
  BPF_PROG_TYPE_TRACEPOINT,
  BPF_PROG_TYPE_XDP,
  BPF_PROG_TYPE_PERF_EVENT,
  BPF_PROG_TYPE_CGROUP_SKB,
  BPF_PROG_TYPE_CGROUP_SOCK,
  BPF_PROG_TYPE_LWT_IN,
  BPF_PROG_TYPE_LWT_OUT,
  BPF_PROG_TYPE_LWT_XMIT,
  BPF_PROG_TYPE_SOCK_OPS,
  BPF_PROG_TYPE_SK_SKB,
  BPF_PROG_TYPE_CGROUP_DEVICE,
  BPF_PROG_TYPE_SK_MSG,
  BPF_PROG_TYPE_RAW_TRACEPOINT,
  BPF_PROG_TYPE_CGROUP_SOCK_ADDR,
  BPF_PROG_TYPE_LWT_SEG6LOCAL,
  BPF_PROG_TYPE_LIRC_MODE2,
  BPF_PROG_TYPE_SK_REUSEPORT,
  BPF_PROG_TYPE_FLOW_DISSECTOR,
  BPF_PROG_TYPE_CGROUP_SYSCTL,
  BPF_PROG_TYPE_RAW_TRACEPOINT_WRITABLE,
  BPF_PROG_TYPE_CGROUP_SOCKOPT,
  BPF_PROG_TYPE_TRACING,
};

enum bpf_attach_type {
  BPF_CGROUP_INET_INGRESS,
  BPF_CGROUP_INET_EGRESS,
  BPF_CGROUP_INET_SOCK_CREATE,
  BPF_CGROUP_SOCK_OPS,
  BPF_SK_SKB_STREAM_PARSER,
  BPF_SK_SKB_STREAM_VERDICT,
  BPF_CGROUP_DEVICE,
  BPF_SK_MSG_VERDICT,
  BPF_CGROUP_INET4_BIND,
  BPF_CGROUP_INET6_BIND,
  BPF_CGROUP_INET4_CONNECT,
  BPF_CGROUP_INET6_CONNECT,
  BPF_CGROUP_INET4_POST_BIND,
  BPF_CGROUP_INET6_POST_BIND,
  BPF_CGROUP_UDP4_SENDMSG,
  BPF_CGROUP_UDP6_SENDMSG,
  BPF_LIRC_MODE2,
  BPF_FLOW_DISSECTOR,
  BPF_CGROUP_SYSCTL,
  BPF_CGROUP_UDP4_RECVMSG,
  BPF_CGROUP_UDP6_RECVMSG,
  BPF_CGROUP_GETSOCKOPT,
  BPF_CGROUP_SETSOCKOPT,
  BPF_TRACE_RAW_TP,
  BPF_TRACE_FENTRY,
  BPF_TRACE_FEXIT,
  __MAX_BPF_ATTACH_TYPE
};

#define MAX_BPF_ATTACH_TYPE __MAX_BPF_ATTACH_TYPE

/* cgroup-bpf attach flags used in BPF_PROG_ATTACH command
 *
 * NONE(default): No further bpf programs allowed in the subtree.
 *
 * BPF_F_ALLOW_OVERRIDE: If a sub-cgroup installs some bpf program,
 * the program in this cgroup yields to sub-cgroup program.
 *
 * BPF_F_ALLOW_MULTI: If a sub-cgroup installs some bpf program,
 * that cgroup program gets run in addition to the program in this cgroup.
 *
 * Only one program is allowed to be attached to a cgroup with
 * NONE or BPF_F_ALLOW_OVERRIDE flag.
 * Attaching another program on top of NONE or BPF_F_ALLOW_OVERRIDE will
 * release old program and attach the new one. Attach flags has to match.
 *
 * Multiple programs are allowed to be attached to a cgroup with
 * BPF_F_ALLOW_MULTI flag. They are executed in FIFO order
 * (those that were attached first, run first)
 * The programs of sub-cgroup are executed first, then programs of
 * this cgroup and then programs of parent cgroup.
 * When children program makes decision (like picking TCP CA or sock bind)
 * parent program has a chance to override it.
 *
 * A cgroup with MULTI or OVERRIDE flag allows any attach flags in sub-cgroups.
 * A cgroup with NONE doesn't allow any programs in sub-cgroups.
 * Ex1:
 * cgrp1 (MULTI progs A, B) ->
 *    cgrp2 (OVERRIDE prog C) ->
 *      cgrp3 (MULTI prog D) ->
 *        cgrp4 (OVERRIDE prog E) ->
 *          cgrp5 (NONE prog F)
 * the event in cgrp5 triggers execution of F,D,A,B in that order.
 * if prog F is detached, the execution is E,D,A,B
 * if prog F and D are detached, the execution is E,A,B
 * if prog F, E and D are detached, the execution is C,A,B
 *
 * All eligible programs are executed regardless of return code from
 * earlier programs.
 */
#define BPF_F_ALLOW_OVERRIDE (1U << 0)
#define BPF_F_ALLOW_MULTI (1U << 1)

/* If BPF_F_STRICT_ALIGNMENT is used in BPF_PROG_LOAD command, the
 * verifier will perform strict alignment checking as if the kernel
 * has been built with CONFIG_EFFICIENT_UNALIGNED_ACCESS not set,
 * and NET_IP_ALIGN defined to 2.
 */
#define BPF_F_STRICT_ALIGNMENT (1U << 0)

/* If BPF_F_ANY_ALIGNMENT is used in BPF_PROF_LOAD command, the
 * verifier will allow any alignment whatsoever.  On platforms
 * with strict alignment requirements for loads ands stores (such
 * as sparc and mips) the verifier validates that all loads and
 * stores provably follow this requirement.  This flag turns that
 * checking and enforcement off.
 *
 * It is mostly used for testing when we want to validate the
 * context and memory access aspects of the verifier, but because
 * of an unaligned access the alignment check would trigger before
 * the one we are interested in.
 */
#define BPF_F_ANY_ALIGNMENT (1U << 1)

/* BPF_F_TEST_RND_HI32 is used in BPF_PROG_LOAD command for testing purpose.
 * Verifier does sub-register def/use analysis and identifies instructions whose
 * def only matters for low 32-bit, high 32-bit is never referenced later
 * through implicit zero extension. Therefore verifier notifies JIT back-ends
 * that it is safe to ignore clearing high 32-bit for these instructions. This
 * saves some back-ends a lot of code-gen. However such optimization is not
 * necessary on some arches, for example x86_64, arm64 etc, whose JIT back-ends
 * hence hasn't used verifier's analysis result. But, we really want to have a
 * way to be able to verify the correctness of the described optimization on
 * x86_64 on which testsuites are frequently exercised.
 *
 * So, this flag is introduced. Once it is set, verifier will randomize high
 * 32-bit for those instructions who has been identified as safe to ignore them.
 * Then, if verifier is not doing correct analysis, such randomization will
 * regress tests to expose bugs.
 */
#define BPF_F_TEST_RND_HI32 (1U << 2)

/* The verifier internal test flag. Behavior is undefined */
#define BPF_F_TEST_STATE_FREQ (1U << 3)

/* When BPF ldimm64's insn[0].src_reg != 0 then this can have
 * two extensions:
 *
 * insn[0].src_reg:  BPF_PSEUDO_MAP_FD   BPF_PSEUDO_MAP_VALUE
 * insn[0].imm:      map fd              map fd
 * insn[1].imm:      0                   offset into value
 * insn[0].off:      0                   0
 * insn[1].off:      0                   0
 * ldimm64 rewrite:  address of map      address of map[0]+offset
 * verifier type:    CONST_PTR_TO_MAP    PTR_TO_MAP_VALUE
 */
#define BPF_PSEUDO_MAP_FD 1
#define BPF_PSEUDO_MAP_VALUE 2

/* when bpf_call->src_reg == BPF_PSEUDO_CALL, bpf_call->imm == pc-relative
 * offset to another bpf function
 */
#define BPF_PSEUDO_CALL 1

/* flags for BPF_MAP_UPDATE_ELEM command */
#define BPF_ANY 0 /* create new element or update existing */
#define BPF_NOEXIST 1 /* create new element if it didn't exist */
#define BPF_EXIST 2 /* update existing element */
#define BPF_F_LOCK 4 /* spin_lock-ed map_lookup/map_update */

/* flags for BPF_MAP_CREATE command */
#define BPF_F_NO_PREALLOC (1U << 0)
/* Instead of having one common LRU list in the
 * BPF_MAP_TYPE_LRU_[PERCPU_]HASH map, use a percpu LRU list
 * which can scale and perform better.
 * Note, the LRU nodes (including free nodes) cannot be moved
 * across different LRU lists.
 */
#define BPF_F_NO_COMMON_LRU (1U << 1)
/* Specify numa node during map creation */
#define BPF_F_NUMA_NODE (1U << 2)

#define BPF_OBJ_NAME_LEN 16U

/* Flags for accessing BPF object from syscall side. */
#define BPF_F_RDONLY (1U << 3)
#define BPF_F_WRONLY (1U << 4)

/* Flag for stack_map, store build_id+offset instead of pointer */
#define BPF_F_STACK_BUILD_ID (1U << 5)

/* Zero-initialize hash function seed. This should only be used for testing. */
#define BPF_F_ZERO_SEED (1U << 6)

/* Flags for accessing BPF object from program side. */
#define BPF_F_RDONLY_PROG (1U << 7)
#define BPF_F_WRONLY_PROG (1U << 8)

/* Clone map from listener for newly accepted socket */
#define BPF_F_CLONE (1U << 9)

/* Enable memory-mapping BPF map */
#define BPF_F_MMAPABLE (1U << 10)

/* flags for BPF_PROG_QUERY */
#define BPF_F_QUERY_EFFECTIVE (1U << 0)

enum bpf_stack_build_id_status {
  /* user space need an empty entry to identify end of a trace */
  BPF_STACK_BUILD_ID_EMPTY = 0,
  /* with valid build_id and offset */
  BPF_STACK_BUILD_ID_VALID = 1,
  /* couldn't get build_id, fallback to ip */
  BPF_STACK_BUILD_ID_IP = 2,
};

#define BPF_BUILD_ID_SIZE 20
struct bpf_stack_build_id {
  __s32 status;
  unsigned char build_id[BPF_BUILD_ID_SIZE];
  union {
    __u64 offset;
    __u64 ip;
  };
};

union bpf_attr {
  struct { /* anonymous struct used by BPF_MAP_CREATE command */
    __u32 map_type; /* one of enum bpf_map_type */
    __u32 key_size; /* size of key in bytes */
    __u32 value_size; /* size of value in bytes */
    __u32 max_entries; /* max number of entries in a map */
    __u32 map_flags; /* BPF_MAP_CREATE related
                      * flags defined above.
                      */
    __u32 inner_map_fd; /* fd pointing to the inner map */
    __u32 numa_node; /* numa node (effective only if
                      * BPF_F_NUMA_NODE is set).
                      */
    char map_name[BPF_OBJ_NAME_LEN];
    __u32 map_ifindex; /* ifindex of netdev to create on */
    __u32 btf_fd; /* fd pointing to a BTF type data */
    __u32 btf_key_type_id; /* BTF type_id of the key */
    __u32 btf_value_type_id; /* BTF type_id of the value */
  };

  struct { /* anonymous struct used by BPF_MAP_*_ELEM commands */
    __u32 map_fd;
    __aligned_u64 key;
    union {
      __aligned_u64 value;
      __aligned_u64 next_key;
    };
    __u64 flags;
  };

  struct { /* anonymous struct used by BPF_PROG_LOAD command */
    __u32 prog_type; /* one of enum bpf_prog_type */
    __u32 insn_cnt;
    __aligned_u64 insns;
    __aligned_u64 license;
    __u32 log_level; /* verbosity level of verifier */
    __u32 log_size; /* size of user buffer */
    __aligned_u64 log_buf; /* user supplied buffer */
    __u32 kern_version; /* not used */
    __u32 prog_flags;
    char prog_name[BPF_OBJ_NAME_LEN];
    __u32 prog_ifindex; /* ifindex of netdev to prep for */
    /* For some prog types expected attach type must be known at
     * load time to verify attach type specific parts of prog
     * (context accesses, allowed helpers, etc).
     */
    __u32 expected_attach_type;
    __u32 prog_btf_fd; /* fd pointing to BTF type data */
    __u32 func_info_rec_size; /* userspace bpf_func_info size */
    __aligned_u64 func_info; /* func info */
    __u32 func_info_cnt; /* number of bpf_func_info records */
    __u32 line_info_rec_size; /* userspace bpf_line_info size */
    __aligned_u64 line_info; /* line info */
    __u32 line_info_cnt; /* number of bpf_line_info records */
    __u32 attach_btf_id; /* in-kernel BTF type id to attach to */
    __u32 attach_prog_fd; /* 0 to attach to vmlinux */
  };

  struct { /* anonymous struct used by BPF_OBJ_* commands */
    __aligned_u64 pathname;
    __u32 bpf_fd;
    __u32 file_flags;
  };

  struct { /* anonymous struct used by BPF_PROG_ATTACH/DETACH commands */
    __u32 target_fd; /* container object to attach to */
    __u32 attach_bpf_fd; /* eBPF program to attach */
    __u32 attach_type;
    __u32 attach_flags;
  };

  struct { /* anonymous struct used by BPF_PROG_TEST_RUN command */
    __u32 prog_fd;
    __u32 retval;
    __u32 data_size_in; /* input: len of data_in */
    __u32 data_size_out; /* input/output: len of data_out
                          *   returns ENOSPC if data_out
                          *   is too small.
                          */
    __aligned_u64 data_in;
    __aligned_u64 data_out;
    __u32 repeat;
    __u32 duration;
    __u32 ctx_size_in; /* input: len of ctx_in */
    __u32 ctx_size_out; /* input/output: len of ctx_out
                         *   returns ENOSPC if ctx_out
                         *   is too small.
                         */
    __aligned_u64 ctx_in;
    __aligned_u64 ctx_out;
  } test;

  struct { /* anonymous struct used by BPF_*_GET_*_ID */
    union {
      __u32 start_id;
      __u32 prog_id;
      __u32 map_id;
      __u32 btf_id;
    };
    __u32 next_id;
    __u32 open_flags;
  };

  struct { /* anonymous struct used by BPF_OBJ_GET_INFO_BY_FD */
    __u32 bpf_fd;
    __u32 info_len;
    __aligned_u64 info;
  } info;

  struct { /* anonymous struct used by BPF_PROG_QUERY command */
    __u32 target_fd; /* container object to query */
    __u32 attach_type;
    __u32 query_flags;
    __u32 attach_flags;
    __aligned_u64 prog_ids;
    __u32 prog_cnt;
  } query;

  struct {
    __u64 name;
    __u32 prog_fd;
  } raw_tracepoint;

  struct { /* anonymous struct for BPF_BTF_LOAD */
    __aligned_u64 btf;
    __aligned_u64 btf_log_buf;
    __u32 btf_size;
    __u32 btf_log_size;
    __u32 btf_log_level;
  };

  struct {
    __u32 pid; /* input: pid */
    __u32 fd; /* input: fd */
    __u32 flags; /* input: flags */
    __u32 buf_len; /* input/output: buf len */
    __aligned_u64 buf; /* input/output:
                        *   tp_name for tracepoint
                        *   symbol for kprobe
                        *   filename for uprobe
                        */
    __u32 prog_id; /* output: prod_id */
    __u32 fd_type; /* output: BPF_FD_TYPE_* */
    __u64 probe_offset; /* output: probe_offset */
    __u64 probe_addr; /* output: probe_addr */
  } task_fd_query;
} __attribute__((aligned(8)));

/* The description below is an attempt at providing documentation to eBPF
 * developers about the multiple available eBPF helper functions. It can be
 * parsed and used to produce a manual page. The workflow is the following,
 * and requires the rst2man utility:
 *
 *     $ ./scripts/bpf_helpers_doc.py \
 *             --filename include/uapi/linux/bpf.h > /tmp/bpf-helpers.rst
 *     $ rst2man /tmp/bpf-helpers.rst > /tmp/bpf-helpers.7
 *     $ man /tmp/bpf-helpers.7
 *
 * Note that in order to produce this external documentation, some RST
 * formatting is used in the descriptions to get "bold" and "italics" in
 * manual pages. Also note that the few trailing white spaces are
 * intentional, removing them would break paragraphs for rst2man.
 *
 * Start of BPF helper function descriptions:
 *
 * void *bpf_map_lookup_elem(struct bpf_map *map, const void *key)
 *  Description
 *    Perform a lookup in *map* for an entry associated to *key*.
 *  Return
 *    Map value associated to *key*, or **NULL** if no entry was
 *    found.
 *
 * int bpf_map_update_elem(struct bpf_map *map, const void *key, const void
 * *value, u64 flags) Description Add or update the value of the entry
 * associated to *key* in *map* with *value*. *flags* is one of:
 *
 *    **BPF_NOEXIST**
 *      The entry for *key* must not exist in the map.
 *    **BPF_EXIST**
 *      The entry for *key* must already exist in the map.
 *    **BPF_ANY**
 *      No condition on the existence of the entry for *key*.
 *
 *    Flag value **BPF_NOEXIST** cannot be used for maps of types
 *    **BPF_MAP_TYPE_ARRAY** or **BPF_MAP_TYPE_PERCPU_ARRAY**  (all
 *    elements always exist), the helper would return an error.
 *  Return
 *    0 on success, or a negative error in case of failure.
 *
 * int bpf_map_delete_elem(struct bpf_map *map, const void *key)
 *  Description
 *    Delete entry with *key* from *map*.
 *  Return
 *    0 on success, or a negative error in case of failure.
 *
 * int bpf_probe_read(void *dst, u32 size, const void *unsafe_ptr)
 *  Description
 *    For tracing programs, safely attempt to read *size* bytes from
 *    kernel space address *unsafe_ptr* and store the data in *dst*.
 *
 *    Generally, use bpf_probe_read_user() or bpf_probe_read_kernel()
 *    instead.
 *  Return
 *    0 on success, or a negative error in case of failure.
 *
 * u64 bpf_ktime_get_ns(void)
 *  Description
 *    Return the time elapsed since system boot, in nanoseconds.
 *  Return
 *    Current *ktime*.
 *
 * int bpf_trace_printk(const char *fmt, u32 fmt_size, ...)
 *  Description
 *    This helper is a "printk()-like" facility for debugging. It
 *    prints a message defined by format *fmt* (of size *fmt_size*)
 *    to file *\/sys/kernel/debug/tracing/trace* from DebugFS, if
 *    available. It can take up to three additional **u64**
 *    arguments (as an eBPF helpers, the total number of arguments is
 *    limited to five).
 *
 *    Each time the helper is called, it appends a line to the trace.
 *    Lines are discarded while *\/sys/kernel/debug/tracing/trace* is
 *    open, use *\/sys/kernel/debug/tracing/trace_pipe* to avoid this.
 *    The format of the trace is customizable, and the exact output
 *    one will get depends on the options set in
 *    *\/sys/kernel/debug/tracing/trace_options* (see also the
 *    *README* file under the same directory). However, it usually
 *    defaults to something like:
 *
 *    ::
 *
 *      telnet-470   [001] .N.. 419421.045894: 0x00000001: <formatted msg>
 *
 *    In the above:
 *
 *      * ``telnet`` is the name of the current task.
 *      * ``470`` is the PID of the current task.
 *      * ``001`` is the CPU number on which the task is
 *        running.
 *      * In ``.N..``, each character refers to a set of
 *        options (whether irqs are enabled, scheduling
 *        options, whether hard/softirqs are running, level of
 *        preempt_disabled respectively). **N** means that
 *        **TIF_NEED_RESCHED** and **PREEMPT_NEED_RESCHED**
 *        are set.
 *      * ``419421.045894`` is a timestamp.
 *      * ``0x00000001`` is a fake value used by BPF for the
 *        instruction pointer register.
 *      * ``<formatted msg>`` is the message formatted with
 *        *fmt*.
 *
 *    The conversion specifiers supported by *fmt* are similar, but
 *    more limited than for printk(). They are **%d**, **%i**,
 *    **%u**, **%x**, **%ld**, **%li**, **%lu**, **%lx**, **%lld**,
 *    **%lli**, **%llu**, **%llx**, **%p**, **%s**. No modifier (size
 *    of field, padding with zeroes, etc.) is available, and the
 *    helper will return **-EINVAL** (but print nothing) if it
 *    encounters an unknown specifier.
 *
 *    Also, note that **bpf_trace_printk**\ () is slow, and should
 *    only be used for debugging purposes. For this reason, a notice
 *    bloc (spanning several lines) is printed to kernel logs and
 *    states that the helper should not be used "for production use"
 *    the first time this helper is used (or more precisely, when
 *    **trace_printk**\ () buffers are allocated). For passing values
 *    to user space, perf events should be preferred.
 *  Return
 *    The number of bytes written to the buffer, or a negative error
 *    in case of failure.
 *
 * u32 bpf_get_prandom_u32(void)
 *  Description
 *    Get a pseudo-random number.
 *
 *    From a security point of view, this helper uses its own
 *    pseudo-random internal state, and cannot be used to infer the
 *    seed of other random functions in the kernel. However, it is
 *    essential to note that the generator used by the helper is not
 *    cryptographically secure.
 *  Return
 *    A random 32-bit unsigned value.
 *
 * u32 bpf_get_smp_processor_id(void)
 *  Description
 *    Get the SMP (symmetric multiprocessing) processor id. Note that
 *    all programs run with preemption disabled, which means that the
 *    SMP processor id is stable during all the execution of the
 *    program.
 *  Return
 *    The SMP id of the processor running the program.
 *
 * int bpf_skb_store_bytes(struct sk_buff *skb, u32 offset, const void *from,
 * u32 len, u64 flags) Description Store *len* bytes from address *from* into
 * the packet associated to *skb*, at *offset*. *flags* are a combination of
 *    **BPF_F_RECOMPUTE_CSUM** (automatically recompute the
 *    checksum for the packet after storing the bytes) and
 *    **BPF_F_INVALIDATE_HASH** (set *skb*\ **->hash**, *skb*\
 *    **->swhash** and *skb*\ **->l4hash** to 0).
 *
 *    A call to this helper is susceptible to change the underlying
 *    packet buffer. Therefore, at load time, all checks on pointers
 *    previously done by the verifier are invalidated and must be
 *    performed again, if the helper is used in combination with
 *    direct packet access.
 *  Return
 *    0 on success, or a negative error in case of failure.
 *
 * int bpf_l3_csum_replace(struct sk_buff *skb, u32 offset, u64 from, u64 to,
 * u64 size) Description Recompute the layer 3 (e.g. IP) checksum for the packet
 *    associated to *skb*. Computation is incremental, so the helper
 *    must know the former value of the header field that was
 *    modified (*from*), the new value of this field (*to*), and the
 *    number of bytes (2 or 4) for this field, stored in *size*.
 *    Alternatively, it is possible to store the difference between
 *    the previous and the new values of the header field in *to*, by
 *    setting *from* and *size* to 0. For both methods, *offset*
 *    indicates the location of the IP checksum within the packet.
 *
 *    This helper works in combination with **bpf_csum_diff**\ (),
 *    which does not update the checksum in-place, but offers more
 *    flexibility and can handle sizes larger than 2 or 4 for the
 *    checksum to update.
 *
 *    A call to this helper is susceptible to change the underlying
 *    packet buffer. Therefore, at load time, all checks on pointers
 *    previously done by the verifier are invalidated and must be
 *    performed again, if the helper is used in combination with
 *    direct packet access.
 *  Return
 *    0 on success, or a negative error in case of failure.
 *
 * int bpf_l4_csum_replace(struct sk_buff *skb, u32 offset, u64 from, u64 to,
 * u64 flags) Description Recompute the layer 4 (e.g. TCP, UDP or ICMP) checksum
 * for the packet associated to *skb*. Computation is incremental, so the helper
 * must know the former value of the header field that was modified (*from*),
 * the new value of this field (*to*), and the number of bytes (2 or 4) for this
 * field, stored on the lowest four bits of *flags*. Alternatively, it is
 * possible to store the difference between the previous and the new values of
 * the header field in *to*, by setting *from* and the four lowest bits of
 * *flags* to 0. For both methods, *offset* indicates the location of the IP
 * checksum within the packet. In addition to the size of the field, *flags* can
 * be added (bitwise OR) actual flags. With **BPF_F_MARK_MANGLED_0**, a null
 * checksum is left untouched (unless **BPF_F_MARK_ENFORCE** is added as well),
 * and for updates resulting in a null checksum the value is set to
 *    **CSUM_MANGLED_0** instead. Flag **BPF_F_PSEUDO_HDR** indicates
 *    the checksum is to be computed against a pseudo-header.
 *
 *    This helper works in combination with **bpf_csum_diff**\ (),
 *    which does not update the checksum in-place, but offers more
 *    flexibility and can handle sizes larger than 2 or 4 for the
 *    checksum to update.
 *
 *    A call to this helper is susceptible to change the underlying
 *    packet buffer. Therefore, at load time, all checks on pointers
 *    previously done by the verifier are invalidated and must be
 *    performed again, if the helper is used in combination with
 *    direct packet access.
 *  Return
 *    0 on success, or a negative error in case of failure.
 *
 * int bpf_tail_call(void *ctx, struct bpf_map *prog_array_map, u32 index)
 *  Description
 *    This special helper is used to trigger a "tail call", or in
 *    other words, to jump into another eBPF program. The same stack
 *    frame is used (but values on stack and in registers for the
 *    caller are not accessible to the callee). This mechanism allows
 *    for program chaining, either for raising the maximum number of
 *    available eBPF instructions, or to execute given programs in
 *    conditional blocks. For security reasons, there is an upper
 *    limit to the number of successive tail calls that can be
 *    performed.
 *
 *    Upon call of this helper, the program attempts to jump into a
 *    program referenced at index *index* in *prog_array_map*, a
 *    special map of type **BPF_MAP_TYPE_PROG_ARRAY**, and passes
 *    *ctx*, a pointer to the context.
 *
 *    If the call succeeds, the kernel immediately runs the first
 *    instruction of the new program. This is not a function call,
 *    and it never returns to the previous program. If the call
 *    fails, then the helper has no effect, and the caller continues
 *    to run its subsequent instructions. A call can fail if the
 *    destination program for the jump does not exist (i.e. *index*
 *    is superior to the number of entries in *prog_array_map*), or
 *    if the maximum number of tail calls has been reached for this
 *    chain of programs. This limit is defined in the kernel by the
 *    macro **MAX_TAIL_CALL_CNT** (not accessible to user space),
 *    which is currently set to 32.
 *  Return
 *    0 on success, or a negative error in case of failure.
 *
 * int bpf_clone_redirect(struct sk_buff *skb, u32 ifindex, u64 flags)
 *  Description
 *    Clone and redirect the packet associated to *skb* to another
 *    net device of index *ifindex*. Both ingress and egress
 *    interfaces can be used for redirection. The **BPF_F_INGRESS**
 *    value in *flags* is used to make the distinction (ingress path
 *    is selected if the flag is present, egress path otherwise).
 *    This is the only flag supported for now.
 *
 *    In comparison with **bpf_redirect**\ () helper,
 *    **bpf_clone_redirect**\ () has the associated cost of
 *    duplicating the packet buffer, but this can be executed out of
 *    the eBPF program. Conversely, **bpf_redirect**\ () is more
 *    efficient, but it is handled through an action code where the
 *    redirection happens only after the eBPF program has returned.
 *
 *    A call to this helper is susceptible to change the underlying
 *    packet buffer. Therefore, at load time, all checks on pointers
 *    previously done by the verifier are invalidated and must be
 *    performed again, if the helper is used in combination with
 *    direct packet access.
 *  Return
 *    0 on success, or a negative error in case of failure.
 *
 * u64 bpf_get_current_pid_tgid(void)
 *  Return
 *    A 64-bit integer containing the current tgid and pid, and
 *    created as such:
 *    *current_task*\ **->tgid << 32 \|**
 *    *current_task*\ **->pid**.
 *
 * u64 bpf_get_current_uid_gid(void)
 *  Return
 *    A 64-bit integer containing the current GID and UID, and
 *    created as such: *current_gid* **<< 32 \|** *current_uid*.
 *
 * int bpf_get_current_comm(void *buf, u32 size_of_buf)
 *  Description
 *    Copy the **comm** attribute of the current task into *buf* of
 *    *size_of_buf*. The **comm** attribute contains the name of
 *    the executable (excluding the path) for the current task. The
 *    *size_of_buf* must be strictly positive. On success, the
 *    helper makes sure that the *buf* is NUL-terminated. On failure,
 *    it is filled with zeroes.
 *  Return
 *    0 on success, or a negative error in case of failure.
 *
 * u32 bpf_get_cgroup_classid(struct sk_buff *skb)
 *  Description
 *    Retrieve the classid for the current task, i.e. for the net_cls
 *    cgroup to which *skb* belongs.
 *
 *    This helper can be used on TC egress path, but not on ingress.
 *
 *    The net_cls cgroup provides an interface to tag network packets
 *    based on a user-provided identifier for all traffic coming from
 *    the tasks belonging to the related cgroup. See also the related
 *    kernel documentation, available from the Linux sources in file
 *    *Documentation/admin-guide/cgroup-v1/net_cls.rst*.
 *
 *    The Linux kernel has two versions for cgroups: there are
 *    cgroups v1 and cgroups v2. Both are available to users, who can
 *    use a mixture of them, but note that the net_cls cgroup is for
 *    cgroup v1 only. This makes it incompatible with BPF programs
 *    run on cgroups, which is a cgroup-v2-only feature (a socket can
 *    only hold data for one version of cgroups at a time).
 *
 *    This helper is only available is the kernel was compiled with
 *    the **CONFIG_CGROUP_NET_CLASSID** configuration option set to
 *    "**y**" or to "**m**".
 *  Return
 *    The classid, or 0 for the default unconfigured classid.
 *
 * int bpf_skb_vlan_push(struct sk_buff *skb, __be16 vlan_proto, u16 vlan_tci)
 *  Description
 *    Push a *vlan_tci* (VLAN tag control information) of protocol
 *    *vlan_proto* to the packet associated to *skb*, then update
 *    the checksum. Note that if *vlan_proto* is different from
 *    **ETH_P_8021Q** and **ETH_P_8021AD**, it is considered to
 *    be **ETH_P_8021Q**.
 *
 *    A call to this helper is susceptible to change the underlying
 *    packet buffer. Therefore, at load time, all checks on pointers
 *    previously done by the verifier are invalidated and must be
 *    performed again, if the helper is used in combination with
 *    direct packet access.
 *  Return
 *    0 on success, or a negative error in case of failure.
 *
 * int bpf_skb_vlan_pop(struct sk_buff *skb)
 *  Description
 *    Pop a VLAN header from the packet associated to *skb*.
 *
 *    A call to this helper is susceptible to change the underlying
 *    packet buffer. Therefore, at load time, all checks on pointers
 *    previously done by the verifier are invalidated and must be
 *    performed again, if the helper is used in combination with
 *    direct packet access.
 *  Return
 *    0 on success, or a negative error in case of failure.
 *
 * int bpf_skb_get_tunnel_key(struct sk_buff *skb, struct bpf_tunnel_key *key,
 * u32 size, u64 flags) Description Get tunnel metadata. This helper takes a
 * pointer *key* to an empty **struct bpf_tunnel_key** of **size**, that will be
 *    filled with tunnel metadata for the packet associated to *skb*.
 *    The *flags* can be set to **BPF_F_TUNINFO_IPV6**, which
 *    indicates that the tunnel is based on IPv6 protocol instead of
 *    IPv4.
 *
 *    The **struct bpf_tunnel_key** is an object that generalizes the
 *    principal parameters used by various tunneling protocols into a
 *    single struct. This way, it can be used to easily make a
 *    decision based on the contents of the encapsulation header,
 *    "summarized" in this struct. In particular, it holds the IP
 *    address of the remote end (IPv4 or IPv6, depending on the case)
 *    in *key*\ **->remote_ipv4** or *key*\ **->remote_ipv6**. Also,
 *    this struct exposes the *key*\ **->tunnel_id**, which is
 *    generally mapped to a VNI (Virtual Network Identifier), making
 *    it programmable together with the **bpf_skb_set_tunnel_key**\
 *    () helper.
 *
 *    Let's imagine that the following code is part of a program
 *    attached to the TC ingress interface, on one end of a GRE
 *    tunnel, and is supposed to filter out all messages coming from
 *    remote ends with IPv4 address other than 10.0.0.1:
 *
 *    ::
 *
 *      int ret;
 *      struct bpf_tunnel_key key = {};
 *
 *      ret = bpf_skb_get_tunnel_key(skb, &key, sizeof(key), 0);
 *      if (ret < 0)
 *        return TC_ACT_SHOT; // drop packet
 *
 *      if (key.remote_ipv4 != 0x0a000001)
 *        return TC_ACT_SHOT; // drop packet
 *
 *      return TC_ACT_OK;   // accept packet
 *
 *    This interface can also be used with all encapsulation devices
 *    that can operate in "collect metadata" mode: instead of having
 *    one network device per specific configuration, the "collect
 *    metadata" mode only requires a single device where the
 *    configuration can be extracted from this helper.
 *
 *    This can be used together with various tunnels such as VXLan,
 *    Geneve, GRE or IP in IP (IPIP).
 *  Return
 *    0 on success, or a negative error in case of failure.
 *
 * int bpf_skb_set_tunnel_key(struct sk_buff *skb, struct bpf_tunnel_key *key,
 * u32 size, u64 flags) Description Populate tunnel metadata for packet
 * associated to *skb.* The tunnel metadata is set to the contents of *key*, of
 * *size*. The *flags* can be set to a combination of the following values:
 *
 *    **BPF_F_TUNINFO_IPV6**
 *      Indicate that the tunnel is based on IPv6 protocol
 *      instead of IPv4.
 *    **BPF_F_ZERO_CSUM_TX**
 *      For IPv4 packets, add a flag to tunnel metadata
 *      indicating that checksum computation should be skipped
 *      and checksum set to zeroes.
 *    **BPF_F_DONT_FRAGMENT**
 *      Add a flag to tunnel metadata indicating that the
 *      packet should not be fragmented.
 *    **BPF_F_SEQ_NUMBER**
 *      Add a flag to tunnel metadata indicating that a
 *      sequence number should be added to tunnel header before
 *      sending the packet. This flag was added for GRE
 *      encapsulation, but might be used with other protocols
 *      as well in the future.
 *
 *    Here is a typical usage on the transmit path:
 *
 *    ::
 *
 *      struct bpf_tunnel_key key;
 *           populate key ...
 *      bpf_skb_set_tunnel_key(skb, &key, sizeof(key), 0);
 *      bpf_clone_redirect(skb, vxlan_dev_ifindex, 0);
 *
 *    See also the description of the **bpf_skb_get_tunnel_key**\ ()
 *    helper for additional information.
 *  Return
 *    0 on success, or a negative error in case of failure.
 *
 * u64 bpf_perf_event_read(struct bpf_map *map, u64 flags)
 *  Description
 *    Read the value of a perf event counter. This helper relies on a
 *    *map* of type **BPF_MAP_TYPE_PERF_EVENT_ARRAY**. The nature of
 *    the perf event counter is selected when *map* is updated with
 *    perf event file descriptors. The *map* is an array whose size
 *    is the number of available CPUs, and each cell contains a value
 *    relative to one CPU. The value to retrieve is indicated by
 *    *flags*, that contains the index of the CPU to look up, masked
 *    with **BPF_F_INDEX_MASK**. Alternatively, *flags* can be set to
 *    **BPF_F_CURRENT_CPU** to indicate that the value for the
 *    current CPU should be retrieved.
 *
 *    Note that before Linux 4.13, only hardware perf event can be
 *    retrieved.
 *
 *    Also, be aware that the newer helper
 *    **bpf_perf_event_read_value**\ () is recommended over
 *    **bpf_perf_event_read**\ () in general. The latter has some ABI
 *    quirks where error and counter value are used as a return code
 *    (which is wrong to do since ranges may overlap). This issue is
 *    fixed with **bpf_perf_event_read_value**\ (), which at the same
 *    time provides more features over the **bpf_perf_event_read**\
 *    () interface. Please refer to the description of
 *    **bpf_perf_event_read_value**\ () for details.
 *  Return
 *    The value of the perf event counter read from the map, or a
 *    negative error code in case of failure.
 *
 * int bpf_redirect(u32 ifindex, u64 flags)
 *  Description
 *    Redirect the packet to another net device of index *ifindex*.
 *    This helper is somewhat similar to **bpf_clone_redirect**\
 *    (), except that the packet is not cloned, which provides
 *    increased performance.
 *
 *    Except for XDP, both ingress and egress interfaces can be used
 *    for redirection. The **BPF_F_INGRESS** value in *flags* is used
 *    to make the distinction (ingress path is selected if the flag
 *    is present, egress path otherwise). Currently, XDP only
 *    supports redirection to the egress interface, and accepts no
 *    flag at all.
 *
 *    The same effect can be attained with the more generic
 *    **bpf_redirect_map**\ (), which requires specific maps to be
 *    used but offers better performance.
 *  Return
 *    For XDP, the helper returns **XDP_REDIRECT** on success or
 *    **XDP_ABORTED** on error. For other program types, the values
 *    are **TC_ACT_REDIRECT** on success or **TC_ACT_SHOT** on
 *    error.
 *
 * u32 bpf_get_route_realm(struct sk_buff *skb)
 *  Description
 *    Retrieve the realm or the route, that is to say the
 *    **tclassid** field of the destination for the *skb*. The
 *    indentifier retrieved is a user-provided tag, similar to the
 *    one used with the net_cls cgroup (see description for
 *    **bpf_get_cgroup_classid**\ () helper), but here this tag is
 *    held by a route (a destination entry), not by a task.
 *
 *    Retrieving this identifier works with the clsact TC egress hook
 *    (see also **tc-bpf(8)**), or alternatively on conventional
 *    classful egress qdiscs, but not on TC ingress path. In case of
 *    clsact TC egress hook, this has the advantage that, internally,
 *    the destination entry has not been dropped yet in the transmit
 *    path. Therefore, the destination entry does not need to be
 *    artificially held via **netif_keep_dst**\ () for a classful
 *    qdisc until the *skb* is freed.
 *
 *    This helper is available only if the kernel was compiled with
 *    **CONFIG_IP_ROUTE_CLASSID** configuration option.
 *  Return
 *    The realm of the route for the packet associated to *skb*, or 0
 *    if none was found.
 *
 * int bpf_perf_event_output(void *ctx, struct bpf_map *map, u64 flags, void
 * *data, u64 size) Description Write raw *data* blob into a special BPF perf
 * event held by *map* of type **BPF_MAP_TYPE_PERF_EVENT_ARRAY**. This perf
 *    event must have the following attributes: **PERF_SAMPLE_RAW**
 *    as **sample_type**, **PERF_TYPE_SOFTWARE** as **type**, and
 *    **PERF_COUNT_SW_BPF_OUTPUT** as **config**.
 *
 *    The *flags* are used to indicate the index in *map* for which
 *    the value must be put, masked with **BPF_F_INDEX_MASK**.
 *    Alternatively, *flags* can be set to **BPF_F_CURRENT_CPU**
 *    to indicate that the index of the current CPU core should be
 *    used.
 *
 *    The value to write, of *size*, is passed through eBPF stack and
 *    pointed by *data*.
 *
 *    The context of the program *ctx* needs also be passed to the
 *    helper.
 *
 *    On user space, a program willing to read the values needs to
 *    call **perf_event_open**\ () on the perf event (either for
 *    one or for all CPUs) and to store the file descriptor into the
 *    *map*. This must be done before the eBPF program can send data
 *    into it. An example is available in file
 *    *samples/bpf/trace_output_user.c* in the Linux kernel source
 *    tree (the eBPF program counterpart is in
 *    *samples/bpf/trace_output.bpf.c*).
 *
 *    **bpf_perf_event_output**\ () achieves better performance
 *    than **bpf_trace_printk**\ () for sharing data with user
 *    space, and is much better suitable for streaming data from eBPF
 *    programs.
 *
 *    Note that this helper is not restricted to tracing use cases
 *    and can be used with programs attached to TC or XDP as well,
 *    where it allows for passing data to user space listeners. Data
 *    can be:
 *
 *    * Only custom structs,
 *    * Only the packet payload, or
 *    * A combination of both.
 *  Return
 *    0 on success, or a negative error in case of failure.
 *
 * int bpf_skb_load_bytes(const void *skb, u32 offset, void *to, u32 len)
 *  Description
 *    This helper was provided as an easy way to load data from a
 *    packet. It can be used to load *len* bytes from *offset* from
 *    the packet associated to *skb*, into the buffer pointed by
 *    *to*.
 *
 *    Since Linux 4.7, usage of this helper has mostly been replaced
 *    by "direct packet access", enabling packet data to be
 *    manipulated with *skb*\ **->data** and *skb*\ **->data_end**
 *    pointing respectively to the first byte of packet data and to
 *    the byte after the last byte of packet data. However, it
 *    remains useful if one wishes to read large quantities of data
 *    at once from a packet into the eBPF stack.
 *  Return
 *    0 on success, or a negative error in case of failure.
 *
 * int bpf_get_stackid(void *ctx, struct bpf_map *map, u64 flags)
 *  Description
 *    Walk a user or a kernel stack and return its id. To achieve
 *    this, the helper needs *ctx*, which is a pointer to the context
 *    on which the tracing program is executed, and a pointer to a
 *    *map* of type **BPF_MAP_TYPE_STACK_TRACE**.
 *
 *    The last argument, *flags*, holds the number of stack frames to
 *    skip (from 0 to 255), masked with
 *    **BPF_F_SKIP_FIELD_MASK**. The next bits can be used to set
 *    a combination of the following flags:
 *
 *    **BPF_F_USER_STACK**
 *      Collect a user space stack instead of a kernel stack.
 *    **BPF_F_FAST_STACK_CMP**
 *      Compare stacks by hash only.
 *    **BPF_F_REUSE_STACKID**
 *      If two different stacks hash into the same *stackid*,
 *      discard the old one.
 *
 *    The stack id retrieved is a 32 bit long integer handle which
 *    can be further combined with other data (including other stack
 *    ids) and used as a key into maps. This can be useful for
 *    generating a variety of graphs (such as flame graphs or off-cpu
 *    graphs).
 *
 *    For walking a stack, this helper is an improvement over
 *    **bpf_probe_read**\ (), which can be used with unrolled loops
 *    but is not efficient and consumes a lot of eBPF instructions.
 *    Instead, **bpf_get_stackid**\ () can collect up to
 *    **PERF_MAX_STACK_DEPTH** both kernel and user frames. Note that
 *    this limit can be controlled with the **sysctl** program, and
 *    that it should be manually increased in order to profile long
 *    user stacks (such as stacks for Java programs). To do so, use:
 *
 *    ::
 *
 *      # sysctl kernel.perf_event_max_stack=<new value>
 *  Return
 *    The positive or null stack id on success, or a negative error
 *    in case of failure.
 *
 * s64 bpf_csum_diff(__be32 *from, u32 from_size, __be32 *to, u32 to_size,
 * __wsum seed) Description Compute a checksum difference, from the raw buffer
 * pointed by *from*, of length *from_size* (that must be a multiple of 4),
 *    towards the raw buffer pointed by *to*, of size *to_size*
 *    (same remark). An optional *seed* can be added to the value
 *    (this can be cascaded, the seed may come from a previous call
 *    to the helper).
 *
 *    This is flexible enough to be used in several ways:
 *
 *    * With *from_size* == 0, *to_size* > 0 and *seed* set to
 *      checksum, it can be used when pushing new data.
 *    * With *from_size* > 0, *to_size* == 0 and *seed* set to
 *      checksum, it can be used when removing data from a packet.
 *    * With *from_size* > 0, *to_size* > 0 and *seed* set to 0, it
 *      can be used to compute a diff. Note that *from_size* and
 *      *to_size* do not need to be equal.
 *
 *    This helper can be used in combination with
 *    **bpf_l3_csum_replace**\ () and **bpf_l4_csum_replace**\ (), to
 *    which one can feed in the difference computed with
 *    **bpf_csum_diff**\ ().
 *  Return
 *    The checksum result, or a negative error code in case of
 *    failure.
 *
 * int bpf_skb_get_tunnel_opt(struct sk_buff *skb, void *opt, u32 size)
 *  Description
 *    Retrieve tunnel options metadata for the packet associated to
 *    *skb*, and store the raw tunnel option data to the buffer *opt*
 *    of *size*.
 *
 *    This helper can be used with encapsulation devices that can
 *    operate in "collect metadata" mode (please refer to the related
 *    note in the description of **bpf_skb_get_tunnel_key**\ () for
 *    more details). A particular example where this can be used is
 *    in combination with the Geneve encapsulation protocol, where it
 *    allows for pushing (with **bpf_skb_get_tunnel_opt**\ () helper)
 *    and retrieving arbitrary TLVs (Type-Length-Value headers) from
 *    the eBPF program. This allows for full customization of these
 *    headers.
 *  Return
 *    The size of the option data retrieved.
 *
 * int bpf_skb_set_tunnel_opt(struct sk_buff *skb, void *opt, u32 size)
 *  Description
 *    Set tunnel options metadata for the packet associated to *skb*
 *    to the option data contained in the raw buffer *opt* of *size*.
 *
 *    See also the description of the **bpf_skb_get_tunnel_opt**\ ()
 *    helper for additional information.
 *  Return
 *    0 on success, or a negative error in case of failure.
 *
 * int bpf_skb_change_proto(struct sk_buff *skb, __be16 proto, u64 flags)
 *  Description
 *    Change the protocol of the *skb* to *proto*. Currently
 *    supported are transition from IPv4 to IPv6, and from IPv6 to
 *    IPv4. The helper takes care of the groundwork for the
 *    transition, including resizing the socket buffer. The eBPF
 *    program is expected to fill the new headers, if any, via
 *    **skb_store_bytes**\ () and to recompute the checksums with
 *    **bpf_l3_csum_replace**\ () and **bpf_l4_csum_replace**\
 *    (). The main case for this helper is to perform NAT64
 *    operations out of an eBPF program.
 *
 *    Internally, the GSO type is marked as dodgy so that headers are
 *    checked and segments are recalculated by the GSO/GRO engine.
 *    The size for GSO target is adapted as well.
 *
 *    All values for *flags* are reserved for future usage, and must
 *    be left at zero.
 *
 *    A call to this helper is susceptible to change the underlying
 *    packet buffer. Therefore, at load time, all checks on pointers
 *    previously done by the verifier are invalidated and must be
 *    performed again, if the helper is used in combination with
 *    direct packet access.
 *  Return
 *    0 on success, or a negative error in case of failure.
 *
 * int bpf_skb_change_type(struct sk_buff *skb, u32 type)
 *  Description
 *    Change the packet type for the packet associated to *skb*. This
 *    comes down to setting *skb*\ **->pkt_type** to *type*, except
 *    the eBPF program does not have a write access to *skb*\
 *    **->pkt_type** beside this helper. Using a helper here allows
 *    for graceful handling of errors.
 *
 *    The major use case is to change incoming *skb*s to
 *    **PACKET_HOST** in a programmatic way instead of having to
 *    recirculate via **redirect**\ (..., **BPF_F_INGRESS**), for
 *    example.
 *
 *    Note that *type* only allows certain values. At this time, they
 *    are:
 *
 *    **PACKET_HOST**
 *      Packet is for us.
 *    **PACKET_BROADCAST**
 *      Send packet to all.
 *    **PACKET_MULTICAST**
 *      Send packet to group.
 *    **PACKET_OTHERHOST**
 *      Send packet to someone else.
 *  Return
 *    0 on success, or a negative error in case of failure.
 *
 * int bpf_skb_under_cgroup(struct sk_buff *skb, struct bpf_map *map, u32 index)
 *  Description
 *    Check whether *skb* is a descendant of the cgroup2 held by
 *    *map* of type **BPF_MAP_TYPE_CGROUP_ARRAY**, at *index*.
 *  Return
 *    The return value depends on the result of the test, and can be:
 *
 *    * 0, if the *skb* failed the cgroup2 descendant test.
 *    * 1, if the *skb* succeeded the cgroup2 descendant test.
 *    * A negative error code, if an error occurred.
 *
 * u32 bpf_get_hash_recalc(struct sk_buff *skb)
 *  Description
 *    Retrieve the hash of the packet, *skb*\ **->hash**. If it is
 *    not set, in particular if the hash was cleared due to mangling,
 *    recompute this hash. Later accesses to the hash can be done
 *    directly with *skb*\ **->hash**.
 *
 *    Calling **bpf_set_hash_invalid**\ (), changing a packet
 *    prototype with **bpf_skb_change_proto**\ (), or calling
 *    **bpf_skb_store_bytes**\ () with the
 *    **BPF_F_INVALIDATE_HASH** are actions susceptible to clear
 *    the hash and to trigger a new computation for the next call to
 *    **bpf_get_hash_recalc**\ ().
 *  Return
 *    The 32-bit hash.
 *
 * u64 bpf_get_current_task(void)
 *  Return
 *    A pointer to the current task struct.
 *
 * int bpf_probe_write_user(void *dst, const void *src, u32 len)
 *  Description
 *    Attempt in a safe way to write *len* bytes from the buffer
 *    *src* to *dst* in memory. It only works for threads that are in
 *    user context, and *dst* must be a valid user space address.
 *
 *    This helper should not be used to implement any kind of
 *    security mechanism because of TOC-TOU attacks, but rather to
 *    debug, divert, and manipulate execution of semi-cooperative
 *    processes.
 *
 *    Keep in mind that this feature is meant for experiments, and it
 *    has a risk of crashing the system and running programs.
 *    Therefore, when an eBPF program using this helper is attached,
 *    a warning including PID and process name is printed to kernel
 *    logs.
 *  Return
 *    0 on success, or a negative error in case of failure.
 *
 * int bpf_current_task_under_cgroup(struct bpf_map *map, u32 index)
 *  Description
 *    Check whether the probe is being run is the context of a given
 *    subset of the cgroup2 hierarchy. The cgroup2 to test is held by
 *    *map* of type **BPF_MAP_TYPE_CGROUP_ARRAY**, at *index*.
 *  Return
 *    The return value depends on the result of the test, and can be:
 *
 *    * 0, if the *skb* task belongs to the cgroup2.
 *    * 1, if the *skb* task does not belong to the cgroup2.
 *    * A negative error code, if an error occurred.
 *
 * int bpf_skb_change_tail(struct sk_buff *skb, u32 len, u64 flags)
 *  Description
 *    Resize (trim or grow) the packet associated to *skb* to the
 *    new *len*. The *flags* are reserved for future usage, and must
 *    be left at zero.
 *
 *    The basic idea is that the helper performs the needed work to
 *    change the size of the packet, then the eBPF program rewrites
 *    the rest via helpers like **bpf_skb_store_bytes**\ (),
 *    **bpf_l3_csum_replace**\ (), **bpf_l3_csum_replace**\ ()
 *    and others. This helper is a slow path utility intended for
 *    replies with control messages. And because it is targeted for
 *    slow path, the helper itself can afford to be slow: it
 *    implicitly linearizes, unclones and drops offloads from the
 *    *skb*.
 *
 *    A call to this helper is susceptible to change the underlying
 *    packet buffer. Therefore, at load time, all checks on pointers
 *    previously done by the verifier are invalidated and must be
 *    performed again, if the helper is used in combination with
 *    direct packet access.
 *  Return
 *    0 on success, or a negative error in case of failure.
 *
 * int bpf_skb_pull_data(struct sk_buff *skb, u32 len)
 *  Description
 *    Pull in non-linear data in case the *skb* is non-linear and not
 *    all of *len* are part of the linear section. Make *len* bytes
 *    from *skb* readable and writable. If a zero value is passed for
 *    *len*, then the whole length of the *skb* is pulled.
 *
 *    This helper is only needed for reading and writing with direct
 *    packet access.
 *
 *    For direct packet access, testing that offsets to access
 *    are within packet boundaries (test on *skb*\ **->data_end**) is
 *    susceptible to fail if offsets are invalid, or if the requested
 *    data is in non-linear parts of the *skb*. On failure the
 *    program can just bail out, or in the case of a non-linear
 *    buffer, use a helper to make the data available. The
 *    **bpf_skb_load_bytes**\ () helper is a first solution to access
 *    the data. Another one consists in using **bpf_skb_pull_data**
 *    to pull in once the non-linear parts, then retesting and
 *    eventually access the data.
 *
 *    At the same time, this also makes sure the *skb* is uncloned,
 *    which is a necessary condition for direct write. As this needs
 *    to be an invariant for the write part only, the verifier
 *    detects writes and adds a prologue that is calling
 *    **bpf_skb_pull_data()** to effectively unclone the *skb* from
 *    the very beginning in case it is indeed cloned.
 *
 *    A call to this helper is susceptible to change the underlying
 *    packet buffer. Therefore, at load time, all checks on pointers
 *    previously done by the verifier are invalidated and must be
 *    performed again, if the helper is used in combination with
 *    direct packet access.
 *  Return
 *    0 on success, or a negative error in case of failure.
 *
 * s64 bpf_csum_update(struct sk_buff *skb, __wsum csum)
 *  Description
 *    Add the checksum *csum* into *skb*\ **->csum** in case the
 *    driver has supplied a checksum for the entire packet into that
 *    field. Return an error otherwise. This helper is intended to be
 *    used in combination with **bpf_csum_diff**\ (), in particular
 *    when the checksum needs to be updated after data has been
 *    written into the packet through direct packet access.
 *  Return
 *    The checksum on success, or a negative error code in case of
 *    failure.
 *
 * void bpf_set_hash_invalid(struct sk_buff *skb)
 *  Description
 *    Invalidate the current *skb*\ **->hash**. It can be used after
 *    mangling on headers through direct packet access, in order to
 *    indicate that the hash is outdated and to trigger a
 *    recalculation the next time the kernel tries to access this
 *    hash or when the **bpf_get_hash_recalc**\ () helper is called.
 *
 * int bpf_get_numa_node_id(void)
 *  Description
 *    Return the id of the current NUMA node. The primary use case
 *    for this helper is the selection of sockets for the local NUMA
 *    node, when the program is attached to sockets using the
 *    **SO_ATTACH_REUSEPORT_EBPF** option (see also **socket(7)**),
 *    but the helper is also available to other eBPF program types,
 *    similarly to **bpf_get_smp_processor_id**\ ().
 *  Return
 *    The id of current NUMA node.
 *
 * int bpf_skb_change_head(struct sk_buff *skb, u32 len, u64 flags)
 *  Description
 *    Grows headroom of packet associated to *skb* and adjusts the
 *    offset of the MAC header accordingly, adding *len* bytes of
 *    space. It automatically extends and reallocates memory as
 *    required.
 *
 *    This helper can be used on a layer 3 *skb* to push a MAC header
 *    for redirection into a layer 2 device.
 *
 *    All values for *flags* are reserved for future usage, and must
 *    be left at zero.
 *
 *    A call to this helper is susceptible to change the underlying
 *    packet buffer. Therefore, at load time, all checks on pointers
 *    previously done by the verifier are invalidated and must be
 *    performed again, if the helper is used in combination with
 *    direct packet access.
 *  Return
 *    0 on success, or a negative error in case of failure.
 *
 * int bpf_xdp_adjust_head(struct xdp_buff *xdp_md, int delta)
 *  Description
 *    Adjust (move) *xdp_md*\ **->data** by *delta* bytes. Note that
 *    it is possible to use a negative value for *delta*. This helper
 *    can be used to prepare the packet for pushing or popping
 *    headers.
 *
 *    A call to this helper is susceptible to change the underlying
 *    packet buffer. Therefore, at load time, all checks on pointers
 *    previously done by the verifier are invalidated and must be
 *    performed again, if the helper is used in combination with
 *    direct packet access.
 *  Return
 *    0 on success, or a negative error in case of failure.
 *
 * int bpf_probe_read_str(void *dst, u32 size, const void *unsafe_ptr)
 *  Description
 *    Copy a NUL terminated string from an unsafe kernel address
 *    *unsafe_ptr* to *dst*. See bpf_probe_read_kernel_str() for
 *    more details.
 *
 *    Generally, use bpf_probe_read_user_str() or bpf_probe_read_kernel_str()
 *    instead.
 *  Return
 *    On success, the strictly positive length of the string,
 *    including the trailing NUL character. On error, a negative
 *    value.
 *
 * u64 bpf_get_socket_cookie(struct sk_buff *skb)
 *  Description
 *    If the **struct sk_buff** pointed by *skb* has a known socket,
 *    retrieve the cookie (generated by the kernel) of this socket.
 *    If no cookie has been set yet, generate a new cookie. Once
 *    generated, the socket cookie remains stable for the life of the
 *    socket. This helper can be useful for monitoring per socket
 *    networking traffic statistics as it provides a global socket
 *    identifier that can be assumed unique.
 *  Return
 *    A 8-byte long non-decreasing number on success, or 0 if the
 *    socket field is missing inside *skb*.
 *
 * u64 bpf_get_socket_cookie(struct bpf_sock_addr *ctx)
 *  Description
 *    Equivalent to bpf_get_socket_cookie() helper that accepts
 *    *skb*, but gets socket from **struct bpf_sock_addr** context.
 *  Return
 *    A 8-byte long non-decreasing number.
 *
 * u64 bpf_get_socket_cookie(struct bpf_sock_ops *ctx)
 *  Description
 *    Equivalent to bpf_get_socket_cookie() helper that accepts
 *    *skb*, but gets socket from **struct bpf_sock_ops** context.
 *  Return
 *    A 8-byte long non-decreasing number.
 *
 * u32 bpf_get_socket_uid(struct sk_buff *skb)
 *  Return
 *    The owner UID of the socket associated to *skb*. If the socket
 *    is **NULL**, or if it is not a full socket (i.e. if it is a
 *    time-wait or a request socket instead), **overflowuid** value
 *    is returned (note that **overflowuid** might also be the actual
 *    UID value for the socket).
 *
 * u32 bpf_set_hash(struct sk_buff *skb, u32 hash)
 *  Description
 *    Set the full hash for *skb* (set the field *skb*\ **->hash**)
 *    to value *hash*.
 *  Return
 *    0
 *
 * int bpf_setsockopt(struct bpf_sock_ops *bpf_socket, int level, int optname,
 * void *optval, int optlen) Description Emulate a call to **setsockopt()** on
 * the socket associated to *bpf_socket*, which must be a full socket. The
 * *level* at which the option resides and the name *optname* of the option must
 * be specified, see **setsockopt(2)** for more information. The option value of
 * length *optlen* is pointed by *optval*.
 *
 *    This helper actually implements a subset of **setsockopt()**.
 *    It supports the following *level*\ s:
 *
 *    * **SOL_SOCKET**, which supports the following *optname*\ s:
 *      **SO_RCVBUF**, **SO_SNDBUF**, **SO_MAX_PACING_RATE**,
 *      **SO_PRIORITY**, **SO_RCVLOWAT**, **SO_MARK**.
 *    * **IPPROTO_TCP**, which supports the following *optname*\ s:
 *      **TCP_CONGESTION**, **TCP_BPF_IW**,
 *      **TCP_BPF_SNDCWND_CLAMP**.
 *    * **IPPROTO_IP**, which supports *optname* **IP_TOS**.
 *    * **IPPROTO_IPV6**, which supports *optname* **IPV6_TCLASS**.
 *  Return
 *    0 on success, or a negative error in case of failure.
 *
 * int bpf_skb_adjust_room(struct sk_buff *skb, s32 len_diff, u32 mode, u64
 * flags) Description Grow or shrink the room for data in the packet associated
 * to *skb* by *len_diff*, and according to the selected *mode*.
 *
 *    There are two supported modes at this time:
 *
 *    * **BPF_ADJ_ROOM_MAC**: Adjust room at the mac layer
 *      (room space is added or removed below the layer 2 header).
 *
 *    * **BPF_ADJ_ROOM_NET**: Adjust room at the network layer
 *      (room space is added or removed below the layer 3 header).
 *
 *    The following flags are supported at this time:
 *
 *    * **BPF_F_ADJ_ROOM_FIXED_GSO**: Do not adjust gso_size.
 *      Adjusting mss in this way is not allowed for datagrams.
 *
 *    * **BPF_F_ADJ_ROOM_ENCAP_L3_IPV4**,
 *      **BPF_F_ADJ_ROOM_ENCAP_L3_IPV6**:
 *      Any new space is reserved to hold a tunnel header.
 *      Configure skb offsets and other fields accordingly.
 *
 *    * **BPF_F_ADJ_ROOM_ENCAP_L4_GRE**,
 *      **BPF_F_ADJ_ROOM_ENCAP_L4_UDP**:
 *      Use with ENCAP_L3 flags to further specify the tunnel type.
 *
 *    * **BPF_F_ADJ_ROOM_ENCAP_L2**\ (*len*):
 *      Use with ENCAP_L3/L4 flags to further specify the tunnel
 *      type; *len* is the length of the inner MAC header.
 *
 *    A call to this helper is susceptible to change the underlying
 *    packet buffer. Therefore, at load time, all checks on pointers
 *    previously done by the verifier are invalidated and must be
 *    performed again, if the helper is used in combination with
 *    direct packet access.
 *  Return
 *    0 on success, or a negative error in case of failure.
 *
 * int bpf_redirect_map(struct bpf_map *map, u32 key, u64 flags)
 *  Description
 *    Redirect the packet to the endpoint referenced by *map* at
 *    index *key*. Depending on its type, this *map* can contain
 *    references to net devices (for forwarding packets through other
 *    ports), or to CPUs (for redirecting XDP frames to another CPU;
 *    but this is only implemented for native XDP (with driver
 *    support) as of this writing).
 *
 *    The lower two bits of *flags* are used as the return code if
 *    the map lookup fails. This is so that the return value can be
 *    one of the XDP program return codes up to XDP_TX, as chosen by
 *    the caller. Any higher bits in the *flags* argument must be
 *    unset.
 *
 *    When used to redirect packets to net devices, this helper
 *    provides a high performance increase over **bpf_redirect**\ ().
 *    This is due to various implementation details of the underlying
 *    mechanisms, one of which is the fact that **bpf_redirect_map**\
 *    () tries to send packet as a "bulk" to the device.
 *  Return
 *    **XDP_REDIRECT** on success, or **XDP_ABORTED** on error.
 *
 * int bpf_sk_redirect_map(struct sk_buff *skb, struct bpf_map *map, u32 key,
 * u64 flags) Description Redirect the packet to the socket referenced by *map*
 * (of type
 *    **BPF_MAP_TYPE_SOCKMAP**) at index *key*. Both ingress and
 *    egress interfaces can be used for redirection. The
 *    **BPF_F_INGRESS** value in *flags* is used to make the
 *    distinction (ingress path is selected if the flag is present,
 *    egress path otherwise). This is the only flag supported for now.
 *  Return
 *    **SK_PASS** on success, or **SK_DROP** on error.
 *
 * int bpf_sock_map_update(struct bpf_sock_ops *skops, struct bpf_map *map, void
 * *key, u64 flags) Description Add an entry to, or update a *map* referencing
 * sockets. The *skops* is used as a new value for the entry associated to
 *    *key*. *flags* is one of:
 *
 *    **BPF_NOEXIST**
 *      The entry for *key* must not exist in the map.
 *    **BPF_EXIST**
 *      The entry for *key* must already exist in the map.
 *    **BPF_ANY**
 *      No condition on the existence of the entry for *key*.
 *
 *    If the *map* has eBPF programs (parser and verdict), those will
 *    be inherited by the socket being added. If the socket is
 *    already attached to eBPF programs, this results in an error.
 *  Return
 *    0 on success, or a negative error in case of failure.
 *
 * int bpf_xdp_adjust_meta(struct xdp_buff *xdp_md, int delta)
 *  Description
 *    Adjust the address pointed by *xdp_md*\ **->data_meta** by
 *    *delta* (which can be positive or negative). Note that this
 *    operation modifies the address stored in *xdp_md*\ **->data**,
 *    so the latter must be loaded only after the helper has been
 *    called.
 *
 *    The use of *xdp_md*\ **->data_meta** is optional and programs
 *    are not required to use it. The rationale is that when the
 *    packet is processed with XDP (e.g. as DoS filter), it is
 *    possible to push further meta data along with it before passing
 *    to the stack, and to give the guarantee that an ingress eBPF
 *    program attached as a TC classifier on the same device can pick
 *    this up for further post-processing. Since TC works with socket
 *    buffers, it remains possible to set from XDP the **mark** or
 *    **priority** pointers, or other pointers for the socket buffer.
 *    Having this scratch space generic and programmable allows for
 *    more flexibility as the user is free to store whatever meta
 *    data they need.
 *
 *    A call to this helper is susceptible to change the underlying
 *    packet buffer. Therefore, at load time, all checks on pointers
 *    previously done by the verifier are invalidated and must be
 *    performed again, if the helper is used in combination with
 *    direct packet access.
 *  Return
 *    0 on success, or a negative error in case of failure.
 *
 * int bpf_perf_event_read_value(struct bpf_map *map, u64 flags, struct
 * bpf_perf_event_value *buf, u32 buf_size) Description Read the value of a perf
 * event counter, and store it into *buf* of size *buf_size*. This helper relies
 * on a *map* of type
 *    **BPF_MAP_TYPE_PERF_EVENT_ARRAY**. The nature of the perf event
 *    counter is selected when *map* is updated with perf event file
 *    descriptors. The *map* is an array whose size is the number of
 *    available CPUs, and each cell contains a value relative to one
 *    CPU. The value to retrieve is indicated by *flags*, that
 *    contains the index of the CPU to look up, masked with
 *    **BPF_F_INDEX_MASK**. Alternatively, *flags* can be set to
 *    **BPF_F_CURRENT_CPU** to indicate that the value for the
 *    current CPU should be retrieved.
 *
 *    This helper behaves in a way close to
 *    **bpf_perf_event_read**\ () helper, save that instead of
 *    just returning the value observed, it fills the *buf*
 *    structure. This allows for additional data to be retrieved: in
 *    particular, the enabled and running times (in *buf*\
 *    **->enabled** and *buf*\ **->running**, respectively) are
 *    copied. In general, **bpf_perf_event_read_value**\ () is
 *    recommended over **bpf_perf_event_read**\ (), which has some
 *    ABI issues and provides fewer functionalities.
 *
 *    These values are interesting, because hardware PMU (Performance
 *    Monitoring Unit) counters are limited resources. When there are
 *    more PMU based perf events opened than available counters,
 *    kernel will multiplex these events so each event gets certain
 *    percentage (but not all) of the PMU time. In case that
 *    multiplexing happens, the number of samples or counter value
 *    will not reflect the case compared to when no multiplexing
 *    occurs. This makes comparison between different runs difficult.
 *    Typically, the counter value should be normalized before
 *    comparing to other experiments. The usual normalization is done
 *    as follows.
 *
 *    ::
 *
 *      normalized_counter = counter * t_enabled / t_running
 *
 *    Where t_enabled is the time enabled for event and t_running is
 *    the time running for event since last normalization. The
 *    enabled and running times are accumulated since the perf event
 *    open. To achieve scaling factor between two invocations of an
 *    eBPF program, users can can use CPU id as the key (which is
 *    typical for perf array usage model) to remember the previous
 *    value and do the calculation inside the eBPF program.
 *  Return
 *    0 on success, or a negative error in case of failure.
 *
 * int bpf_perf_prog_read_value(struct bpf_perf_event_data *ctx, struct
 * bpf_perf_event_value *buf, u32 buf_size) Description For en eBPF program
 * attached to a perf event, retrieve the value of the event counter associated
 * to *ctx* and store it in the structure pointed by *buf* and of size
 * *buf_size*. Enabled and running times are also stored in the structure (see
 *    description of helper **bpf_perf_event_read_value**\ () for
 *    more details).
 *  Return
 *    0 on success, or a negative error in case of failure.
 *
 * int bpf_getsockopt(struct bpf_sock_ops *bpf_socket, int level, int optname,
 * void *optval, int optlen) Description Emulate a call to **getsockopt()** on
 * the socket associated to *bpf_socket*, which must be a full socket. The
 * *level* at which the option resides and the name *optname* of the option must
 * be specified, see **getsockopt(2)** for more information. The retrieved value
 * is stored in the structure pointed by *opval* and of length *optlen*.
 *
 *    This helper actually implements a subset of **getsockopt()**.
 *    It supports the following *level*\ s:
 *
 *    * **IPPROTO_TCP**, which supports *optname*
 *      **TCP_CONGESTION**.
 *    * **IPPROTO_IP**, which supports *optname* **IP_TOS**.
 *    * **IPPROTO_IPV6**, which supports *optname* **IPV6_TCLASS**.
 *  Return
 *    0 on success, or a negative error in case of failure.
 *
 * int bpf_override_return(struct pt_regs *regs, u64 rc)
 *  Description
 *    Used for error injection, this helper uses kprobes to override
 *    the return value of the probed function, and to set it to *rc*.
 *    The first argument is the context *regs* on which the kprobe
 *    works.
 *
 *    This helper works by setting setting the PC (program counter)
 *    to an override function which is run in place of the original
 *    probed function. This means the probed function is not run at
 *    all. The replacement function just returns with the required
 *    value.
 *
 *    This helper has security implications, and thus is subject to
 *    restrictions. It is only available if the kernel was compiled
 *    with the **CONFIG_BPF_KPROBE_OVERRIDE** configuration
 *    option, and in this case it only works on functions tagged with
 *    **ALLOW_ERROR_INJECTION** in the kernel code.
 *
 *    Also, the helper is only available for the architectures having
 *    the CONFIG_FUNCTION_ERROR_INJECTION option. As of this writing,
 *    x86 architecture is the only one to support this feature.
 *  Return
 *    0
 *
 * int bpf_sock_ops_cb_flags_set(struct bpf_sock_ops *bpf_sock, int argval)
 *  Description
 *    Attempt to set the value of the **bpf_sock_ops_cb_flags** field
 *    for the full TCP socket associated to *bpf_sock_ops* to
 *    *argval*.
 *
 *    The primary use of this field is to determine if there should
 *    be calls to eBPF programs of type
 *    **BPF_PROG_TYPE_SOCK_OPS** at various points in the TCP
 *    code. A program of the same type can change its value, per
 *    connection and as necessary, when the connection is
 *    established. This field is directly accessible for reading, but
 *    this helper must be used for updates in order to return an
 *    error if an eBPF program tries to set a callback that is not
 *    supported in the current kernel.
 *
 *    *argval* is a flag array which can combine these flags:
 *
 *    * **BPF_SOCK_OPS_RTO_CB_FLAG** (retransmission time out)
 *    * **BPF_SOCK_OPS_RETRANS_CB_FLAG** (retransmission)
 *    * **BPF_SOCK_OPS_STATE_CB_FLAG** (TCP state change)
 *    * **BPF_SOCK_OPS_RTT_CB_FLAG** (every RTT)
 *
 *    Therefore, this function can be used to clear a callback flag by
 *    setting the appropriate bit to zero. e.g. to disable the RTO
 *    callback:
 *
 *    **bpf_sock_ops_cb_flags_set(bpf_sock,**
 *      **bpf_sock->bpf_sock_ops_cb_flags & ~BPF_SOCK_OPS_RTO_CB_FLAG)**
 *
 *    Here are some examples of where one could call such eBPF
 *    program:
 *
 *    * When RTO fires.
 *    * When a packet is retransmitted.
 *    * When the connection terminates.
 *    * When a packet is sent.
 *    * When a packet is received.
 *  Return
 *    Code **-EINVAL** if the socket is not a full TCP socket;
 *    otherwise, a positive number containing the bits that could not
 *    be set is returned (which comes down to 0 if all bits were set
 *    as required).
 *
 * int bpf_msg_redirect_map(struct sk_msg_buff *msg, struct bpf_map *map, u32
 * key, u64 flags) Description This helper is used in programs implementing
 * policies at the socket level. If the message *msg* is allowed to pass (i.e.
 * if the verdict eBPF program returns **SK_PASS**), redirect it to the socket
 * referenced by *map* (of type
 *    **BPF_MAP_TYPE_SOCKMAP**) at index *key*. Both ingress and
 *    egress interfaces can be used for redirection. The
 *    **BPF_F_INGRESS** value in *flags* is used to make the
 *    distinction (ingress path is selected if the flag is present,
 *    egress path otherwise). This is the only flag supported for now.
 *  Return
 *    **SK_PASS** on success, or **SK_DROP** on error.
 *
 * int bpf_msg_apply_bytes(struct sk_msg_buff *msg, u32 bytes)
 *  Description
 *    For socket policies, apply the verdict of the eBPF program to
 *    the next *bytes* (number of bytes) of message *msg*.
 *
 *    For example, this helper can be used in the following cases:
 *
 *    * A single **sendmsg**\ () or **sendfile**\ () system call
 *      contains multiple logical messages that the eBPF program is
 *      supposed to read and for which it should apply a verdict.
 *    * An eBPF program only cares to read the first *bytes* of a
 *      *msg*. If the message has a large payload, then setting up
 *      and calling the eBPF program repeatedly for all bytes, even
 *      though the verdict is already known, would create unnecessary
 *      overhead.
 *
 *    When called from within an eBPF program, the helper sets a
 *    counter internal to the BPF infrastructure, that is used to
 *    apply the last verdict to the next *bytes*. If *bytes* is
 *    smaller than the current data being processed from a
 *    **sendmsg**\ () or **sendfile**\ () system call, the first
 *    *bytes* will be sent and the eBPF program will be re-run with
 *    the pointer for start of data pointing to byte number *bytes*
 *    **+ 1**. If *bytes* is larger than the current data being
 *    processed, then the eBPF verdict will be applied to multiple
 *    **sendmsg**\ () or **sendfile**\ () calls until *bytes* are
 *    consumed.
 *
 *    Note that if a socket closes with the internal counter holding
 *    a non-zero value, this is not a problem because data is not
 *    being buffered for *bytes* and is sent as it is received.
 *  Return
 *    0
 *
 * int bpf_msg_cork_bytes(struct sk_msg_buff *msg, u32 bytes)
 *  Description
 *    For socket policies, prevent the execution of the verdict eBPF
 *    program for message *msg* until *bytes* (byte number) have been
 *    accumulated.
 *
 *    This can be used when one needs a specific number of bytes
 *    before a verdict can be assigned, even if the data spans
 *    multiple **sendmsg**\ () or **sendfile**\ () calls. The extreme
 *    case would be a user calling **sendmsg**\ () repeatedly with
 *    1-byte long message segments. Obviously, this is bad for
 *    performance, but it is still valid. If the eBPF program needs
 *    *bytes* bytes to validate a header, this helper can be used to
 *    prevent the eBPF program to be called again until *bytes* have
 *    been accumulated.
 *  Return
 *    0
 *
 * int bpf_msg_pull_data(struct sk_msg_buff *msg, u32 start, u32 end, u64 flags)
 *  Description
 *    For socket policies, pull in non-linear data from user space
 *    for *msg* and set pointers *msg*\ **->data** and *msg*\
 *    **->data_end** to *start* and *end* bytes offsets into *msg*,
 *    respectively.
 *
 *    If a program of type **BPF_PROG_TYPE_SK_MSG** is run on a
 *    *msg* it can only parse data that the (**data**, **data_end**)
 *    pointers have already consumed. For **sendmsg**\ () hooks this
 *    is likely the first scatterlist element. But for calls relying
 *    on the **sendpage** handler (e.g. **sendfile**\ ()) this will
 *    be the range (**0**, **0**) because the data is shared with
 *    user space and by default the objective is to avoid allowing
 *    user space to modify data while (or after) eBPF verdict is
 *    being decided. This helper can be used to pull in data and to
 *    set the start and end pointer to given values. Data will be
 *    copied if necessary (i.e. if data was not linear and if start
 *    and end pointers do not point to the same chunk).
 *
 *    A call to this helper is susceptible to change the underlying
 *    packet buffer. Therefore, at load time, all checks on pointers
 *    previously done by the verifier are invalidated and must be
 *    performed again, if the helper is used in combination with
 *    direct packet access.
 *
 *    All values for *flags* are reserved for future usage, and must
 *    be left at zero.
 *  Return
 *    0 on success, or a negative error in case of failure.
 *
 * int bpf_bind(struct bpf_sock_addr *ctx, struct sockaddr *addr, int addr_len)
 *  Description
 *    Bind the socket associated to *ctx* to the address pointed by
 *    *addr*, of length *addr_len*. This allows for making outgoing
 *    connection from the desired IP address, which can be useful for
 *    example when all processes inside a cgroup should use one
 *    single IP address on a host that has multiple IP configured.
 *
 *    This helper works for IPv4 and IPv6, TCP and UDP sockets. The
 *    domain (*addr*\ **->sa_family**) must be **AF_INET** (or
 *    **AF_INET6**). Looking for a free port to bind to can be
 *    expensive, therefore binding to port is not permitted by the
 *    helper: *addr*\ **->sin_port** (or **sin6_port**, respectively)
 *    must be set to zero.
 *  Return
 *    0 on success, or a negative error in case of failure.
 *
 * int bpf_xdp_adjust_tail(struct xdp_buff *xdp_md, int delta)
 *  Description
 *    Adjust (move) *xdp_md*\ **->data_end** by *delta* bytes. It is
 *    only possible to shrink the packet as of this writing,
 *    therefore *delta* must be a negative integer.
 *
 *    A call to this helper is susceptible to change the underlying
 *    packet buffer. Therefore, at load time, all checks on pointers
 *    previously done by the verifier are invalidated and must be
 *    performed again, if the helper is used in combination with
 *    direct packet access.
 *  Return
 *    0 on success, or a negative error in case of failure.
 *
 * int bpf_skb_get_xfrm_state(struct sk_buff *skb, u32 index, struct
 * bpf_xfrm_state *xfrm_state, u32 size, u64 flags) Description Retrieve the
 * XFRM state (IP transform framework, see also
 *    **ip-xfrm(8)**) at *index* in XFRM "security path" for *skb*.
 *
 *    The retrieved value is stored in the **struct bpf_xfrm_state**
 *    pointed by *xfrm_state* and of length *size*.
 *
 *    All values for *flags* are reserved for future usage, and must
 *    be left at zero.
 *
 *    This helper is available only if the kernel was compiled with
 *    **CONFIG_XFRM** configuration option.
 *  Return
 *    0 on success, or a negative error in case of failure.
 *
 * int bpf_get_stack(void *ctx, void *buf, u32 size, u64 flags)
 *  Description
 *    Return a user or a kernel stack in bpf program provided buffer.
 *    To achieve this, the helper needs *ctx*, which is a pointer
 *    to the context on which the tracing program is executed.
 *    To store the stacktrace, the bpf program provides *buf* with
 *    a nonnegative *size*.
 *
 *    The last argument, *flags*, holds the number of stack frames to
 *    skip (from 0 to 255), masked with
 *    **BPF_F_SKIP_FIELD_MASK**. The next bits can be used to set
 *    the following flags:
 *
 *    **BPF_F_USER_STACK**
 *      Collect a user space stack instead of a kernel stack.
 *    **BPF_F_USER_BUILD_ID**
 *      Collect buildid+offset instead of ips for user stack,
 *      only valid if **BPF_F_USER_STACK** is also specified.
 *
 *    **bpf_get_stack**\ () can collect up to
 *    **PERF_MAX_STACK_DEPTH** both kernel and user frames, subject
 *    to sufficient large buffer size. Note that
 *    this limit can be controlled with the **sysctl** program, and
 *    that it should be manually increased in order to profile long
 *    user stacks (such as stacks for Java programs). To do so, use:
 *
 *    ::
 *
 *      # sysctl kernel.perf_event_max_stack=<new value>
 *  Return
 *    A non-negative value equal to or less than *size* on success,
 *    or a negative error in case of failure.
 *
 * int bpf_skb_load_bytes_relative(const void *skb, u32 offset, void *to, u32
 * len, u32 start_header) Description This helper is similar to
 * **bpf_skb_load_bytes**\ () in that it provides an easy way to load *len*
 * bytes from *offset* from the packet associated to *skb*, into the buffer
 * pointed by *to*. The difference to **bpf_skb_load_bytes**\ () is that a fifth
 * argument *start_header* exists in order to select a base offset to start
 * from. *start_header* can be one of:
 *
 *    **BPF_HDR_START_MAC**
 *      Base offset to load data from is *skb*'s mac header.
 *    **BPF_HDR_START_NET**
 *      Base offset to load data from is *skb*'s network header.
 *
 *    In general, "direct packet access" is the preferred method to
 *    access packet data, however, this helper is in particular useful
 *    in socket filters where *skb*\ **->data** does not always point
 *    to the start of the mac header and where "direct packet access"
 *    is not available.
 *  Return
 *    0 on success, or a negative error in case of failure.
 *
 * int bpf_fib_lookup(void *ctx, struct bpf_fib_lookup *params, int plen, u32
 * flags) Description Do FIB lookup in kernel tables using parameters in
 * *params*. If lookup is successful and result shows packet is to be forwarded,
 * the neighbor tables are searched for the nexthop. If successful (ie., FIB
 * lookup shows forwarding and nexthop is resolved), the nexthop address is
 * returned in ipv4_dst or ipv6_dst based on family, smac is set to mac address
 * of egress device, dmac is set to nexthop mac address, rt_metric is set to
 * metric from route (IPv4/IPv6 only), and ifindex is set to the device index of
 * the nexthop from the FIB lookup.
 *
 *    *plen* argument is the size of the passed in struct.
 *    *flags* argument can be a combination of one or more of the
 *    following values:
 *
 *    **BPF_FIB_LOOKUP_DIRECT**
 *      Do a direct table lookup vs full lookup using FIB
 *      rules.
 *    **BPF_FIB_LOOKUP_OUTPUT**
 *      Perform lookup from an egress perspective (default is
 *      ingress).
 *
 *    *ctx* is either **struct xdp_md** for XDP programs or
 *    **struct sk_buff** tc cls_act programs.
 *  Return
 *    * < 0 if any input argument is invalid
 *    *   0 on success (packet is forwarded, nexthop neighbor exists)
 *    * > 0 one of **BPF_FIB_LKUP_RET_** codes explaining why the
 *      packet is not forwarded or needs assist from full stack
 *
 * int bpf_sock_hash_update(struct bpf_sock_ops *skops, struct bpf_map *map,
 * void *key, u64 flags) Description Add an entry to, or update a sockhash *map*
 * referencing sockets. The *skops* is used as a new value for the entry
 * associated to *key*. *flags* is one of:
 *
 *    **BPF_NOEXIST**
 *      The entry for *key* must not exist in the map.
 *    **BPF_EXIST**
 *      The entry for *key* must already exist in the map.
 *    **BPF_ANY**
 *      No condition on the existence of the entry for *key*.
 *
 *    If the *map* has eBPF programs (parser and verdict), those will
 *    be inherited by the socket being added. If the socket is
 *    already attached to eBPF programs, this results in an error.
 *  Return
 *    0 on success, or a negative error in case of failure.
 *
 * int bpf_msg_redirect_hash(struct sk_msg_buff *msg, struct bpf_map *map, void
 * *key, u64 flags) Description This helper is used in programs implementing
 * policies at the socket level. If the message *msg* is allowed to pass (i.e.
 * if the verdict eBPF program returns **SK_PASS**), redirect it to the socket
 * referenced by *map* (of type
 *    **BPF_MAP_TYPE_SOCKHASH**) using hash *key*. Both ingress and
 *    egress interfaces can be used for redirection. The
 *    **BPF_F_INGRESS** value in *flags* is used to make the
 *    distinction (ingress path is selected if the flag is present,
 *    egress path otherwise). This is the only flag supported for now.
 *  Return
 *    **SK_PASS** on success, or **SK_DROP** on error.
 *
 * int bpf_sk_redirect_hash(struct sk_buff *skb, struct bpf_map *map, void *key,
 * u64 flags) Description This helper is used in programs implementing policies
 * at the skb socket level. If the sk_buff *skb* is allowed to pass (i.e. if the
 * verdeict eBPF program returns **SK_PASS**), redirect it to the socket
 * referenced by *map* (of type
 *    **BPF_MAP_TYPE_SOCKHASH**) using hash *key*. Both ingress and
 *    egress interfaces can be used for redirection. The
 *    **BPF_F_INGRESS** value in *flags* is used to make the
 *    distinction (ingress path is selected if the flag is present,
 *    egress otherwise). This is the only flag supported for now.
 *  Return
 *    **SK_PASS** on success, or **SK_DROP** on error.
 *
 * int bpf_lwt_push_encap(struct sk_buff *skb, u32 type, void *hdr, u32 len)
 *  Description
 *    Encapsulate the packet associated to *skb* within a Layer 3
 *    protocol header. This header is provided in the buffer at
 *    address *hdr*, with *len* its size in bytes. *type* indicates
 *    the protocol of the header and can be one of:
 *
 *    **BPF_LWT_ENCAP_SEG6**
 *      IPv6 encapsulation with Segment Routing Header
 *      (**struct ipv6_sr_hdr**). *hdr* only contains the SRH,
 *      the IPv6 header is computed by the kernel.
 *    **BPF_LWT_ENCAP_SEG6_INLINE**
 *      Only works if *skb* contains an IPv6 packet. Insert a
 *      Segment Routing Header (**struct ipv6_sr_hdr**) inside
 *      the IPv6 header.
 *    **BPF_LWT_ENCAP_IP**
 *      IP encapsulation (GRE/GUE/IPIP/etc). The outer header
 *      must be IPv4 or IPv6, followed by zero or more
 *      additional headers, up to **LWT_BPF_MAX_HEADROOM**
 *      total bytes in all prepended headers. Please note that
 *      if **skb_is_gso**\ (*skb*) is true, no more than two
 *      headers can be prepended, and the inner header, if
 *      present, should be either GRE or UDP/GUE.
 *
 *    **BPF_LWT_ENCAP_SEG6**\ \* types can be called by BPF programs
 *    of type **BPF_PROG_TYPE_LWT_IN**; **BPF_LWT_ENCAP_IP** type can
 *    be called by bpf programs of types **BPF_PROG_TYPE_LWT_IN** and
 *    **BPF_PROG_TYPE_LWT_XMIT**.
 *
 *    A call to this helper is susceptible to change the underlying
 *    packet buffer. Therefore, at load time, all checks on pointers
 *    previously done by the verifier are invalidated and must be
 *    performed again, if the helper is used in combination with
 *    direct packet access.
 *  Return
 *    0 on success, or a negative error in case of failure.
 *
 * int bpf_lwt_seg6_store_bytes(struct sk_buff *skb, u32 offset, const void
 * *from, u32 len) Description Store *len* bytes from address *from* into the
 * packet associated to *skb*, at *offset*. Only the flags, tag and TLVs inside
 * the outermost IPv6 Segment Routing Header can be modified through this
 * helper.
 *
 *    A call to this helper is susceptible to change the underlying
 *    packet buffer. Therefore, at load time, all checks on pointers
 *    previously done by the verifier are invalidated and must be
 *    performed again, if the helper is used in combination with
 *    direct packet access.
 *  Return
 *    0 on success, or a negative error in case of failure.
 *
 * int bpf_lwt_seg6_adjust_srh(struct sk_buff *skb, u32 offset, s32 delta)
 *  Description
 *    Adjust the size allocated to TLVs in the outermost IPv6
 *    Segment Routing Header contained in the packet associated to
 *    *skb*, at position *offset* by *delta* bytes. Only offsets
 *    after the segments are accepted. *delta* can be as well
 *    positive (growing) as negative (shrinking).
 *
 *    A call to this helper is susceptible to change the underlying
 *    packet buffer. Therefore, at load time, all checks on pointers
 *    previously done by the verifier are invalidated and must be
 *    performed again, if the helper is used in combination with
 *    direct packet access.
 *  Return
 *    0 on success, or a negative error in case of failure.
 *
 * int bpf_lwt_seg6_action(struct sk_buff *skb, u32 action, void *param, u32
 * param_len) Description Apply an IPv6 Segment Routing action of type *action*
 * to the packet associated to *skb*. Each action takes a parameter contained at
 * address *param*, and of length *param_len* bytes. *action* can be one of:
 *
 *    **SEG6_LOCAL_ACTION_END_X**
 *      End.X action: Endpoint with Layer-3 cross-connect.
 *      Type of *param*: **struct in6_addr**.
 *    **SEG6_LOCAL_ACTION_END_T**
 *      End.T action: Endpoint with specific IPv6 table lookup.
 *      Type of *param*: **int**.
 *    **SEG6_LOCAL_ACTION_END_B6**
 *      End.B6 action: Endpoint bound to an SRv6 policy.
 *      Type of *param*: **struct ipv6_sr_hdr**.
 *    **SEG6_LOCAL_ACTION_END_B6_ENCAP**
 *      End.B6.Encap action: Endpoint bound to an SRv6
 *      encapsulation policy.
 *      Type of *param*: **struct ipv6_sr_hdr**.
 *
 *    A call to this helper is susceptible to change the underlying
 *    packet buffer. Therefore, at load time, all checks on pointers
 *    previously done by the verifier are invalidated and must be
 *    performed again, if the helper is used in combination with
 *    direct packet access.
 *  Return
 *    0 on success, or a negative error in case of failure.
 *
 * int bpf_rc_repeat(void *ctx)
 *  Description
 *    This helper is used in programs implementing IR decoding, to
 *    report a successfully decoded repeat key message. This delays
 *    the generation of a key up event for previously generated
 *    key down event.
 *
 *    Some IR protocols like NEC have a special IR message for
 *    repeating last button, for when a button is held down.
 *
 *    The *ctx* should point to the lirc sample as passed into
 *    the program.
 *
 *    This helper is only available is the kernel was compiled with
 *    the **CONFIG_BPF_LIRC_MODE2** configuration option set to
 *    "**y**".
 *  Return
 *    0
 *
 * int bpf_rc_keydown(void *ctx, u32 protocol, u64 scancode, u32 toggle)
 *  Description
 *    This helper is used in programs implementing IR decoding, to
 *    report a successfully decoded key press with *scancode*,
 *    *toggle* value in the given *protocol*. The scancode will be
 *    translated to a keycode using the rc keymap, and reported as
 *    an input key down event. After a period a key up event is
 *    generated. This period can be extended by calling either
 *    **bpf_rc_keydown**\ () again with the same values, or calling
 *    **bpf_rc_repeat**\ ().
 *
 *    Some protocols include a toggle bit, in case the button was
 *    released and pressed again between consecutive scancodes.
 *
 *    The *ctx* should point to the lirc sample as passed into
 *    the program.
 *
 *    The *protocol* is the decoded protocol number (see
 *    **enum rc_proto** for some predefined values).
 *
 *    This helper is only available is the kernel was compiled with
 *    the **CONFIG_BPF_LIRC_MODE2** configuration option set to
 *    "**y**".
 *  Return
 *    0
 *
 * u64 bpf_skb_cgroup_id(struct sk_buff *skb)
 *  Description
 *    Return the cgroup v2 id of the socket associated with the *skb*.
 *    This is roughly similar to the **bpf_get_cgroup_classid**\ ()
 *    helper for cgroup v1 by providing a tag resp. identifier that
 *    can be matched on or used for map lookups e.g. to implement
 *    policy. The cgroup v2 id of a given path in the hierarchy is
 *    exposed in user space through the f_handle API in order to get
 *    to the same 64-bit id.
 *
 *    This helper can be used on TC egress path, but not on ingress,
 *    and is available only if the kernel was compiled with the
 *    **CONFIG_SOCK_CGROUP_DATA** configuration option.
 *  Return
 *    The id is returned or 0 in case the id could not be retrieved.
 *
 * u64 bpf_get_current_cgroup_id(void)
 *  Return
 *    A 64-bit integer containing the current cgroup id based
 *    on the cgroup within which the current task is running.
 *
 * void *bpf_get_local_storage(void *map, u64 flags)
 *  Description
 *    Get the pointer to the local storage area.
 *    The type and the size of the local storage is defined
 *    by the *map* argument.
 *    The *flags* meaning is specific for each map type,
 *    and has to be 0 for cgroup local storage.
 *
 *    Depending on the BPF program type, a local storage area
 *    can be shared between multiple instances of the BPF program,
 *    running simultaneously.
 *
 *    A user should care about the synchronization by himself.
 *    For example, by using the **BPF_STX_XADD** instruction to alter
 *    the shared data.
 *  Return
 *    A pointer to the local storage area.
 *
 * int bpf_sk_select_reuseport(struct sk_reuseport_md *reuse, struct bpf_map
 * *map, void *key, u64 flags) Description Select a **SO_REUSEPORT** socket from
 * a
 *    **BPF_MAP_TYPE_REUSEPORT_ARRAY** *map*.
 *    It checks the selected socket is matching the incoming
 *    request in the socket buffer.
 *  Return
 *    0 on success, or a negative error in case of failure.
 *
 * u64 bpf_skb_ancestor_cgroup_id(struct sk_buff *skb, int ancestor_level)
 *  Description
 *    Return id of cgroup v2 that is ancestor of cgroup associated
 *    with the *skb* at the *ancestor_level*.  The root cgroup is at
 *    *ancestor_level* zero and each step down the hierarchy
 *    increments the level. If *ancestor_level* == level of cgroup
 *    associated with *skb*, then return value will be same as that
 *    of **bpf_skb_cgroup_id**\ ().
 *
 *    The helper is useful to implement policies based on cgroups
 *    that are upper in hierarchy than immediate cgroup associated
 *    with *skb*.
 *
 *    The format of returned id and helper limitations are same as in
 *    **bpf_skb_cgroup_id**\ ().
 *  Return
 *    The id is returned or 0 in case the id could not be retrieved.
 *
 * struct bpf_sock *bpf_sk_lookup_tcp(void *ctx, struct bpf_sock_tuple *tuple,
 * u32 tuple_size, u64 netns, u64 flags) Description Look for TCP socket
 * matching *tuple*, optionally in a child network namespace *netns*. The return
 * value must be checked, and if non-**NULL**, released via
 * **bpf_sk_release**\ ().
 *
 *    The *ctx* should point to the context of the program, such as
 *    the skb or socket (depending on the hook in use). This is used
 *    to determine the base network namespace for the lookup.
 *
 *    *tuple_size* must be one of:
 *
 *    **sizeof**\ (*tuple*\ **->ipv4**)
 *      Look for an IPv4 socket.
 *    **sizeof**\ (*tuple*\ **->ipv6**)
 *      Look for an IPv6 socket.
 *
 *    If the *netns* is a negative signed 32-bit integer, then the
 *    socket lookup table in the netns associated with the *ctx* will
 *    will be used. For the TC hooks, this is the netns of the device
 *    in the skb. For socket hooks, this is the netns of the socket.
 *    If *netns* is any other signed 32-bit value greater than or
 *    equal to zero then it specifies the ID of the netns relative to
 *    the netns associated with the *ctx*. *netns* values beyond the
 *    range of 32-bit integers are reserved for future use.
 *
 *    All values for *flags* are reserved for future usage, and must
 *    be left at zero.
 *
 *    This helper is available only if the kernel was compiled with
 *    **CONFIG_NET** configuration option.
 *  Return
 *    Pointer to **struct bpf_sock**, or **NULL** in case of failure.
 *    For sockets with reuseport option, the **struct bpf_sock**
 *    result is from *reuse*\ **->socks**\ [] using the hash of the
 *    tuple.
 *
 * struct bpf_sock *bpf_sk_lookup_udp(void *ctx, struct bpf_sock_tuple *tuple,
 * u32 tuple_size, u64 netns, u64 flags) Description Look for UDP socket
 * matching *tuple*, optionally in a child network namespace *netns*. The return
 * value must be checked, and if non-**NULL**, released via
 * **bpf_sk_release**\ ().
 *
 *    The *ctx* should point to the context of the program, such as
 *    the skb or socket (depending on the hook in use). This is used
 *    to determine the base network namespace for the lookup.
 *
 *    *tuple_size* must be one of:
 *
 *    **sizeof**\ (*tuple*\ **->ipv4**)
 *      Look for an IPv4 socket.
 *    **sizeof**\ (*tuple*\ **->ipv6**)
 *      Look for an IPv6 socket.
 *
 *    If the *netns* is a negative signed 32-bit integer, then the
 *    socket lookup table in the netns associated with the *ctx* will
 *    will be used. For the TC hooks, this is the netns of the device
 *    in the skb. For socket hooks, this is the netns of the socket.
 *    If *netns* is any other signed 32-bit value greater than or
 *    equal to zero then it specifies the ID of the netns relative to
 *    the netns associated with the *ctx*. *netns* values beyond the
 *    range of 32-bit integers are reserved for future use.
 *
 *    All values for *flags* are reserved for future usage, and must
 *    be left at zero.
 *
 *    This helper is available only if the kernel was compiled with
 *    **CONFIG_NET** configuration option.
 *  Return
 *    Pointer to **struct bpf_sock**, or **NULL** in case of failure.
 *    For sockets with reuseport option, the **struct bpf_sock**
 *    result is from *reuse*\ **->socks**\ [] using the hash of the
 *    tuple.
 *
 * int bpf_sk_release(struct bpf_sock *sock)
 *  Description
 *    Release the reference held by *sock*. *sock* must be a
 *    non-**NULL** pointer that was returned from
 *    **bpf_sk_lookup_xxx**\ ().
 *  Return
 *    0 on success, or a negative error in case of failure.
 *
 * int bpf_map_push_elem(struct bpf_map *map, const void *value, u64 flags)
 *  Description
 *    Push an element *value* in *map*. *flags* is one of:
 *
 *    **BPF_EXIST**
 *      If the queue/stack is full, the oldest element is
 *      removed to make room for this.
 *  Return
 *    0 on success, or a negative error in case of failure.
 *
 * int bpf_map_pop_elem(struct bpf_map *map, void *value)
 *  Description
 *    Pop an element from *map*.
 *  Return
 *    0 on success, or a negative error in case of failure.
 *
 * int bpf_map_peek_elem(struct bpf_map *map, void *value)
 *  Description
 *    Get an element from *map* without removing it.
 *  Return
 *    0 on success, or a negative error in case of failure.
 *
 * int bpf_msg_push_data(struct sk_msg_buff *msg, u32 start, u32 len, u64 flags)
 *  Description
 *    For socket policies, insert *len* bytes into *msg* at offset
 *    *start*.
 *
 *    If a program of type **BPF_PROG_TYPE_SK_MSG** is run on a
 *    *msg* it may want to insert metadata or options into the *msg*.
 *    This can later be read and used by any of the lower layer BPF
 *    hooks.
 *
 *    This helper may fail if under memory pressure (a malloc
 *    fails) in these cases BPF programs will get an appropriate
 *    error and BPF programs will need to handle them.
 *  Return
 *    0 on success, or a negative error in case of failure.
 *
 * int bpf_msg_pop_data(struct sk_msg_buff *msg, u32 start, u32 len, u64 flags)
 *  Description
 *    Will remove *len* bytes from a *msg* starting at byte *start*.
 *    This may result in **ENOMEM** errors under certain situations if
 *    an allocation and copy are required due to a full ring buffer.
 *    However, the helper will try to avoid doing the allocation
 *    if possible. Other errors can occur if input parameters are
 *    invalid either due to *start* byte not being valid part of *msg*
 *    payload and/or *pop* value being to large.
 *  Return
 *    0 on success, or a negative error in case of failure.
 *
 * int bpf_rc_pointer_rel(void *ctx, s32 rel_x, s32 rel_y)
 *  Description
 *    This helper is used in programs implementing IR decoding, to
 *    report a successfully decoded pointer movement.
 *
 *    The *ctx* should point to the lirc sample as passed into
 *    the program.
 *
 *    This helper is only available is the kernel was compiled with
 *    the **CONFIG_BPF_LIRC_MODE2** configuration option set to
 *    "**y**".
 *  Return
 *    0
 *
 * int bpf_spin_lock(struct bpf_spin_lock *lock)
 *  Description
 *    Acquire a spinlock represented by the pointer *lock*, which is
 *    stored as part of a value of a map. Taking the lock allows to
 *    safely update the rest of the fields in that value. The
 *    spinlock can (and must) later be released with a call to
 *    **bpf_spin_unlock**\ (\ *lock*\ ).
 *
 *    Spinlocks in BPF programs come with a number of restrictions
 *    and constraints:
 *
 *    * **bpf_spin_lock** objects are only allowed inside maps of
 *      types **BPF_MAP_TYPE_HASH** and **BPF_MAP_TYPE_ARRAY** (this
 *      list could be extended in the future).
 *    * BTF description of the map is mandatory.
 *    * The BPF program can take ONE lock at a time, since taking two
 *      or more could cause dead locks.
 *    * Only one **struct bpf_spin_lock** is allowed per map element.
 *    * When the lock is taken, calls (either BPF to BPF or helpers)
 *      are not allowed.
 *    * The **BPF_LD_ABS** and **BPF_LD_IND** instructions are not
 *      allowed inside a spinlock-ed region.
 *    * The BPF program MUST call **bpf_spin_unlock**\ () to release
 *      the lock, on all execution paths, before it returns.
 *    * The BPF program can access **struct bpf_spin_lock** only via
 *      the **bpf_spin_lock**\ () and **bpf_spin_unlock**\ ()
 *      helpers. Loading or storing data into the **struct
 *      bpf_spin_lock** *lock*\ **;** field of a map is not allowed.
 *    * To use the **bpf_spin_lock**\ () helper, the BTF description
 *      of the map value must be a struct and have **struct
 *      bpf_spin_lock** *anyname*\ **;** field at the top level.
 *      Nested lock inside another struct is not allowed.
 *    * The **struct bpf_spin_lock** *lock* field in a map value must
 *      be aligned on a multiple of 4 bytes in that value.
 *    * Syscall with command **BPF_MAP_LOOKUP_ELEM** does not copy
 *      the **bpf_spin_lock** field to user space.
 *    * Syscall with command **BPF_MAP_UPDATE_ELEM**, or update from
 *      a BPF program, do not update the **bpf_spin_lock** field.
 *    * **bpf_spin_lock** cannot be on the stack or inside a
 *      networking packet (it can only be inside of a map values).
 *    * **bpf_spin_lock** is available to root only.
 *    * Tracing programs and socket filter programs cannot use
 *      **bpf_spin_lock**\ () due to insufficient preemption checks
 *      (but this may change in the future).
 *    * **bpf_spin_lock** is not allowed in inner maps of map-in-map.
 *  Return
 *    0
 *
 * int bpf_spin_unlock(struct bpf_spin_lock *lock)
 *  Description
 *    Release the *lock* previously locked by a call to
 *    **bpf_spin_lock**\ (\ *lock*\ ).
 *  Return
 *    0
 *
 * struct bpf_sock *bpf_sk_fullsock(struct bpf_sock *sk)
 *  Description
 *    This helper gets a **struct bpf_sock** pointer such
 *    that all the fields in this **bpf_sock** can be accessed.
 *  Return
 *    A **struct bpf_sock** pointer on success, or **NULL** in
 *    case of failure.
 *
 * struct bpf_tcp_sock *bpf_tcp_sock(struct bpf_sock *sk)
 *  Description
 *    This helper gets a **struct bpf_tcp_sock** pointer from a
 *    **struct bpf_sock** pointer.
 *  Return
 *    A **struct bpf_tcp_sock** pointer on success, or **NULL** in
 *    case of failure.
 *
 * int bpf_skb_ecn_set_ce(struct sk_buff *skb)
 *  Description
 *    Set ECN (Explicit Congestion Notification) field of IP header
 *    to **CE** (Congestion Encountered) if current value is **ECT**
 *    (ECN Capable Transport). Otherwise, do nothing. Works with IPv6
 *    and IPv4.
 *  Return
 *    1 if the **CE** flag is set (either by the current helper call
 *    or because it was already present), 0 if it is not set.
 *
 * struct bpf_sock *bpf_get_listener_sock(struct bpf_sock *sk)
 *  Description
 *    Return a **struct bpf_sock** pointer in **TCP_LISTEN** state.
 *    **bpf_sk_release**\ () is unnecessary and not allowed.
 *  Return
 *    A **struct bpf_sock** pointer on success, or **NULL** in
 *    case of failure.
 *
 * struct bpf_sock *bpf_skc_lookup_tcp(void *ctx, struct bpf_sock_tuple *tuple,
 * u32 tuple_size, u64 netns, u64 flags) Description Look for TCP socket
 * matching *tuple*, optionally in a child network namespace *netns*. The return
 * value must be checked, and if non-**NULL**, released via
 * **bpf_sk_release**\ ().
 *
 *    This function is identical to **bpf_sk_lookup_tcp**\ (), except
 *    that it also returns timewait or request sockets. Use
 *    **bpf_sk_fullsock**\ () or **bpf_tcp_sock**\ () to access the
 *    full structure.
 *
 *    This helper is available only if the kernel was compiled with
 *    **CONFIG_NET** configuration option.
 *  Return
 *    Pointer to **struct bpf_sock**, or **NULL** in case of failure.
 *    For sockets with reuseport option, the **struct bpf_sock**
 *    result is from *reuse*\ **->socks**\ [] using the hash of the
 *    tuple.
 *
 * int bpf_tcp_check_syncookie(struct bpf_sock *sk, void *iph, u32 iph_len,
 * struct tcphdr *th, u32 th_len) Description Check whether *iph* and *th*
 * contain a valid SYN cookie ACK for the listening socket in *sk*.
 *
 *    *iph* points to the start of the IPv4 or IPv6 header, while
 *    *iph_len* contains **sizeof**\ (**struct iphdr**) or
 *    **sizeof**\ (**struct ip6hdr**).
 *
 *    *th* points to the start of the TCP header, while *th_len*
 *    contains **sizeof**\ (**struct tcphdr**).
 *
 *  Return
 *    0 if *iph* and *th* are a valid SYN cookie ACK, or a negative
 *    error otherwise.
 *
 * int bpf_sysctl_get_name(struct bpf_sysctl *ctx, char *buf, size_t buf_len,
 * u64 flags) Description Get name of sysctl in /proc/sys/ and copy it into
 * provided by program buffer *buf* of size *buf_len*.
 *
 *    The buffer is always NUL terminated, unless it's zero-sized.
 *
 *    If *flags* is zero, full name (e.g. "net/ipv4/tcp_mem") is
 *    copied. Use **BPF_F_SYSCTL_BASE_NAME** flag to copy base name
 *    only (e.g. "tcp_mem").
 *  Return
 *    Number of character copied (not including the trailing NUL).
 *
 *    **-E2BIG** if the buffer wasn't big enough (*buf* will contain
 *    truncated name in this case).
 *
 * int bpf_sysctl_get_current_value(struct bpf_sysctl *ctx, char *buf, size_t
 * buf_len) Description Get current value of sysctl as it is presented in
 * /proc/sys (incl. newline, etc), and copy it as a string into provided by
 * program buffer *buf* of size *buf_len*.
 *
 *    The whole value is copied, no matter what file position user
 *    space issued e.g. sys_read at.
 *
 *    The buffer is always NUL terminated, unless it's zero-sized.
 *  Return
 *    Number of character copied (not including the trailing NUL).
 *
 *    **-E2BIG** if the buffer wasn't big enough (*buf* will contain
 *    truncated name in this case).
 *
 *    **-EINVAL** if current value was unavailable, e.g. because
 *    sysctl is uninitialized and read returns -EIO for it.
 *
 * int bpf_sysctl_get_new_value(struct bpf_sysctl *ctx, char *buf, size_t
 * buf_len) Description Get new value being written by user space to sysctl
 * (before the actual write happens) and copy it as a string into provided by
 * program buffer *buf* of size *buf_len*.
 *
 *    User space may write new value at file position > 0.
 *
 *    The buffer is always NUL terminated, unless it's zero-sized.
 *  Return
 *    Number of character copied (not including the trailing NUL).
 *
 *    **-E2BIG** if the buffer wasn't big enough (*buf* will contain
 *    truncated name in this case).
 *
 *    **-EINVAL** if sysctl is being read.
 *
 * int bpf_sysctl_set_new_value(struct bpf_sysctl *ctx, const char *buf, size_t
 * buf_len) Description Override new value being written by user space to sysctl
 * with value provided by program in buffer *buf* of size *buf_len*.
 *
 *    *buf* should contain a string in same form as provided by user
 *    space on sysctl write.
 *
 *    User space may write new value at file position > 0. To override
 *    the whole sysctl value file position should be set to zero.
 *  Return
 *    0 on success.
 *
 *    **-E2BIG** if the *buf_len* is too big.
 *
 *    **-EINVAL** if sysctl is being read.
 *
 * int bpf_strtol(const char *buf, size_t buf_len, u64 flags, long *res)
 *  Description
 *    Convert the initial part of the string from buffer *buf* of
 *    size *buf_len* to a long integer according to the given base
 *    and save the result in *res*.
 *
 *    The string may begin with an arbitrary amount of white space
 *    (as determined by **isspace**\ (3)) followed by a single
 *    optional '**-**' sign.
 *
 *    Five least significant bits of *flags* encode base, other bits
 *    are currently unused.
 *
 *    Base must be either 8, 10, 16 or 0 to detect it automatically
 *    similar to user space **strtol**\ (3).
 *  Return
 *    Number of characters consumed on success. Must be positive but
 *    no more than *buf_len*.
 *
 *    **-EINVAL** if no valid digits were found or unsupported base
 *    was provided.
 *
 *    **-ERANGE** if resulting value was out of range.
 *
 * int bpf_strtoul(const char *buf, size_t buf_len, u64 flags, unsigned long
 * *res) Description Convert the initial part of the string from buffer *buf* of
 *    size *buf_len* to an unsigned long integer according to the
 *    given base and save the result in *res*.
 *
 *    The string may begin with an arbitrary amount of white space
 *    (as determined by **isspace**\ (3)).
 *
 *    Five least significant bits of *flags* encode base, other bits
 *    are currently unused.
 *
 *    Base must be either 8, 10, 16 or 0 to detect it automatically
 *    similar to user space **strtoul**\ (3).
 *  Return
 *    Number of characters consumed on success. Must be positive but
 *    no more than *buf_len*.
 *
 *    **-EINVAL** if no valid digits were found or unsupported base
 *    was provided.
 *
 *    **-ERANGE** if resulting value was out of range.
 *
 * void *bpf_sk_storage_get(struct bpf_map *map, struct bpf_sock *sk, void
 * *value, u64 flags) Description Get a bpf-local-storage from a *sk*.
 *
 *    Logically, it could be thought of getting the value from
 *    a *map* with *sk* as the **key**.  From this
 *    perspective,  the usage is not much different from
 *    **bpf_map_lookup_elem**\ (*map*, **&**\ *sk*) except this
 *    helper enforces the key must be a full socket and the map must
 *    be a **BPF_MAP_TYPE_SK_STORAGE** also.
 *
 *    Underneath, the value is stored locally at *sk* instead of
 *    the *map*.  The *map* is used as the bpf-local-storage
 *    "type". The bpf-local-storage "type" (i.e. the *map*) is
 *    searched against all bpf-local-storages residing at *sk*.
 *
 *    An optional *flags* (**BPF_SK_STORAGE_GET_F_CREATE**) can be
 *    used such that a new bpf-local-storage will be
 *    created if one does not exist.  *value* can be used
 *    together with **BPF_SK_STORAGE_GET_F_CREATE** to specify
 *    the initial value of a bpf-local-storage.  If *value* is
 *    **NULL**, the new bpf-local-storage will be zero initialized.
 *  Return
 *    A bpf-local-storage pointer is returned on success.
 *
 *    **NULL** if not found or there was an error in adding
 *    a new bpf-local-storage.
 *
 * int bpf_sk_storage_delete(struct bpf_map *map, struct bpf_sock *sk)
 *  Description
 *    Delete a bpf-local-storage from a *sk*.
 *  Return
 *    0 on success.
 *
 *    **-ENOENT** if the bpf-local-storage cannot be found.
 *
 * int bpf_send_signal(u32 sig)
 *  Description
 *    Send signal *sig* to the current task.
 *  Return
 *    0 on success or successfully queued.
 *
 *    **-EBUSY** if work queue under nmi is full.
 *
 *    **-EINVAL** if *sig* is invalid.
 *
 *    **-EPERM** if no permission to send the *sig*.
 *
 *    **-EAGAIN** if bpf program can try again.
 *
 * s64 bpf_tcp_gen_syncookie(struct bpf_sock *sk, void *iph, u32 iph_len, struct
 * tcphdr *th, u32 th_len) Description Try to issue a SYN cookie for the packet
 * with corresponding IP/TCP headers, *iph* and *th*, on the listening socket in
 * *sk*.
 *
 *    *iph* points to the start of the IPv4 or IPv6 header, while
 *    *iph_len* contains **sizeof**\ (**struct iphdr**) or
 *    **sizeof**\ (**struct ip6hdr**).
 *
 *    *th* points to the start of the TCP header, while *th_len*
 *    contains the length of the TCP header.
 *
 *  Return
 *    On success, lower 32 bits hold the generated SYN cookie in
 *    followed by 16 bits which hold the MSS value for that cookie,
 *    and the top 16 bits are unused.
 *
 *    On failure, the returned value is one of the following:
 *
 *    **-EINVAL** SYN cookie cannot be issued due to error
 *
 *    **-ENOENT** SYN cookie should not be issued (no SYN flood)
 *
 *    **-EOPNOTSUPP** kernel configuration does not enable SYN cookies
 *
 *    **-EPROTONOSUPPORT** IP packet version is not 4 or 6
 *
 * int bpf_skb_output(void *ctx, struct bpf_map *map, u64 flags, void *data, u64
 * size) Description Write raw *data* blob into a special BPF perf event held by
 *    *map* of type **BPF_MAP_TYPE_PERF_EVENT_ARRAY**. This perf
 *    event must have the following attributes: **PERF_SAMPLE_RAW**
 *    as **sample_type**, **PERF_TYPE_SOFTWARE** as **type**, and
 *    **PERF_COUNT_SW_BPF_OUTPUT** as **config**.
 *
 *    The *flags* are used to indicate the index in *map* for which
 *    the value must be put, masked with **BPF_F_INDEX_MASK**.
 *    Alternatively, *flags* can be set to **BPF_F_CURRENT_CPU**
 *    to indicate that the index of the current CPU core should be
 *    used.
 *
 *    The value to write, of *size*, is passed through eBPF stack and
 *    pointed by *data*.
 *
 *    *ctx* is a pointer to in-kernel struct sk_buff.
 *
 *    This helper is similar to **bpf_perf_event_output**\ () but
 *    restricted to raw_tracepoint bpf programs.
 *  Return
 *    0 on success, or a negative error in case of failure.
 *
 * int bpf_probe_read_user(void *dst, u32 size, const void *unsafe_ptr)
 *  Description
 *    Safely attempt to read *size* bytes from user space address
 *    *unsafe_ptr* and store the data in *dst*.
 *  Return
 *    0 on success, or a negative error in case of failure.
 *
 * int bpf_probe_read_kernel(void *dst, u32 size, const void *unsafe_ptr)
 *  Description
 *    Safely attempt to read *size* bytes from kernel space address
 *    *unsafe_ptr* and store the data in *dst*.
 *  Return
 *    0 on success, or a negative error in case of failure.
 *
 * int bpf_probe_read_user_str(void *dst, u32 size, const void *unsafe_ptr)
 *  Description
 *    Copy a NUL terminated string from an unsafe user address
 *    *unsafe_ptr* to *dst*. The *size* should include the
 *    terminating NUL byte. In case the string length is smaller than
 *    *size*, the target is not padded with further NUL bytes. If the
 *    string length is larger than *size*, just *size*-1 bytes are
 *    copied and the last byte is set to NUL.
 *
 *    On success, the length of the copied string is returned. This
 *    makes this helper useful in tracing programs for reading
 *    strings, and more importantly to get its length at runtime. See
 *    the following snippet:
 *
 *    ::
 *
 *      SEC("kprobe/sys_open")
 *      void bpf_sys_open(struct pt_regs *ctx)
 *      {
 *              char buf[PATHLEN]; // PATHLEN is defined to 256
 *              int res = bpf_probe_read_user_str(buf, sizeof(buf),
 *                                          ctx->di);
 *
 *        // Consume buf, for example push it to
 *        // userspace via bpf_perf_event_output(); we
 *        // can use res (the string length) as event
 *        // size, after checking its boundaries.
 *      }
 *
 *    In comparison, using **bpf_probe_read_user()** helper here
 *    instead to read the string would require to estimate the length
 *    at compile time, and would often result in copying more memory
 *    than necessary.
 *
 *    Another useful use case is when parsing individual process
 *    arguments or individual environment variables navigating
 *    *current*\ **->mm->arg_start** and *current*\
 *    **->mm->env_start**: using this helper and the return value,
 *    one can quickly iterate at the right offset of the memory area.
 *  Return
 *    On success, the strictly positive length of the string,
 *    including the trailing NUL character. On error, a negative
 *    value.
 *
 * int bpf_probe_read_kernel_str(void *dst, u32 size, const void *unsafe_ptr)
 *  Description
 *    Copy a NUL terminated string from an unsafe kernel address *unsafe_ptr*
 *    to *dst*. Same semantics as with bpf_probe_read_user_str() apply.
 *  Return
 *    On success, the strictly positive length of the string, including
 *    the trailing NUL character. On error, a negative value.
 */
#define __BPF_FUNC_MAPPER(FN)                                                  \
  FN(unspec), FN(map_lookup_elem), FN(map_update_elem), FN(map_delete_elem),   \
      FN(probe_read), FN(ktime_get_ns), FN(trace_printk), FN(get_prandom_u32), \
      FN(get_smp_processor_id), FN(skb_store_bytes), FN(l3_csum_replace),      \
      FN(l4_csum_replace), FN(tail_call), FN(clone_redirect),                  \
      FN(get_current_pid_tgid), FN(get_current_uid_gid), FN(get_current_comm), \
      FN(get_cgroup_classid), FN(skb_vlan_push), FN(skb_vlan_pop),             \
      FN(skb_get_tunnel_key), FN(skb_set_tunnel_key), FN(perf_event_read),     \
      FN(redirect), FN(get_route_realm), FN(perf_event_output),                \
      FN(skb_load_bytes), FN(get_stackid), FN(csum_diff),                      \
      FN(skb_get_tunnel_opt), FN(skb_set_tunnel_opt), FN(skb_change_proto),    \
      FN(skb_change_type), FN(skb_under_cgroup), FN(get_hash_recalc),          \
      FN(get_current_task), FN(probe_write_user),                              \
      FN(current_task_under_cgroup), FN(skb_change_tail), FN(skb_pull_data),   \
      FN(csum_update), FN(set_hash_invalid), FN(get_numa_node_id),             \
      FN(skb_change_head), FN(xdp_adjust_head), FN(probe_read_str),            \
      FN(get_socket_cookie), FN(get_socket_uid), FN(set_hash), FN(setsockopt), \
      FN(skb_adjust_room), FN(redirect_map), FN(sk_redirect_map),              \
      FN(sock_map_update), FN(xdp_adjust_meta), FN(perf_event_read_value),     \
      FN(perf_prog_read_value), FN(getsockopt), FN(override_return),           \
      FN(sock_ops_cb_flags_set), FN(msg_redirect_map), FN(msg_apply_bytes),    \
      FN(msg_cork_bytes), FN(msg_pull_data), FN(bind), FN(xdp_adjust_tail),    \
      FN(skb_get_xfrm_state), FN(get_stack), FN(skb_load_bytes_relative),      \
      FN(fib_lookup), FN(sock_hash_update), FN(msg_redirect_hash),             \
      FN(sk_redirect_hash), FN(lwt_push_encap), FN(lwt_seg6_store_bytes),      \
      FN(lwt_seg6_adjust_srh), FN(lwt_seg6_action), FN(rc_repeat),             \
      FN(rc_keydown), FN(skb_cgroup_id), FN(get_current_cgroup_id),            \
      FN(get_local_storage), FN(sk_select_reuseport),                          \
      FN(skb_ancestor_cgroup_id), FN(sk_lookup_tcp), FN(sk_lookup_udp),        \
      FN(sk_release), FN(map_push_elem), FN(map_pop_elem), FN(map_peek_elem),  \
      FN(msg_push_data), FN(msg_pop_data), FN(rc_pointer_rel), FN(spin_lock),  \
      FN(spin_unlock), FN(sk_fullsock), FN(tcp_sock), FN(skb_ecn_set_ce),      \
      FN(get_listener_sock), FN(skc_lookup_tcp), FN(tcp_check_syncookie),      \
      FN(sysctl_get_name), FN(sysctl_get_current_value),                       \
      FN(sysctl_get_new_value), FN(sysctl_set_new_value), FN(strtol),          \
      FN(strtoul), FN(sk_storage_get), FN(sk_storage_delete), FN(send_signal), \
      FN(tcp_gen_syncookie), FN(skb_output), FN(probe_read_user),              \
      FN(probe_read_kernel), FN(probe_read_user_str),                          \
      FN(probe_read_kernel_str),

/* integer value in 'imm' field of BPF_CALL instruction selects which helper
 * function eBPF program intends to call
 */
#define __BPF_ENUM_FN(x) BPF_FUNC_##x
enum bpf_func_id {
  __BPF_FUNC_MAPPER(__BPF_ENUM_FN) __BPF_FUNC_MAX_ID,
};
#undef __BPF_ENUM_FN

/* All flags used by eBPF helper functions, placed here. */

/* BPF_FUNC_skb_store_bytes flags. */
#define BPF_F_RECOMPUTE_CSUM (1ULL << 0)
#define BPF_F_INVALIDATE_HASH (1ULL << 1)

/* BPF_FUNC_l3_csum_replace and BPF_FUNC_l4_csum_replace flags.
 * First 4 bits are for passing the header field size.
 */
#define BPF_F_HDR_FIELD_MASK 0xfULL

/* BPF_FUNC_l4_csum_replace flags. */
#define BPF_F_PSEUDO_HDR (1ULL << 4)
#define BPF_F_MARK_MANGLED_0 (1ULL << 5)
#define BPF_F_MARK_ENFORCE (1ULL << 6)

/* BPF_FUNC_clone_redirect and BPF_FUNC_redirect flags. */
#define BPF_F_INGRESS (1ULL << 0)

/* BPF_FUNC_skb_set_tunnel_key and BPF_FUNC_skb_get_tunnel_key flags. */
#define BPF_F_TUNINFO_IPV6 (1ULL << 0)

/* flags for both BPF_FUNC_get_stackid and BPF_FUNC_get_stack. */
#define BPF_F_SKIP_FIELD_MASK 0xffULL
#define BPF_F_USER_STACK (1ULL << 8)
/* flags used by BPF_FUNC_get_stackid only. */
#define BPF_F_FAST_STACK_CMP (1ULL << 9)
#define BPF_F_REUSE_STACKID (1ULL << 10)
/* flags used by BPF_FUNC_get_stack only. */
#define BPF_F_USER_BUILD_ID (1ULL << 11)

/* BPF_FUNC_skb_set_tunnel_key flags. */
#define BPF_F_ZERO_CSUM_TX (1ULL << 1)
#define BPF_F_DONT_FRAGMENT (1ULL << 2)
#define BPF_F_SEQ_NUMBER (1ULL << 3)

/* BPF_FUNC_perf_event_output, BPF_FUNC_perf_event_read and
 * BPF_FUNC_perf_event_read_value flags.
 */
#define BPF_F_INDEX_MASK 0xffffffffULL
#define BPF_F_CURRENT_CPU BPF_F_INDEX_MASK
/* BPF_FUNC_perf_event_output for sk_buff input context. */
#define BPF_F_CTXLEN_MASK (0xfffffULL << 32)

/* Current network namespace */
#define BPF_F_CURRENT_NETNS (-1L)

/* BPF_FUNC_skb_adjust_room flags. */
#define BPF_F_ADJ_ROOM_FIXED_GSO (1ULL << 0)

#define BPF_ADJ_ROOM_ENCAP_L2_MASK 0xff
#define BPF_ADJ_ROOM_ENCAP_L2_SHIFT 56

#define BPF_F_ADJ_ROOM_ENCAP_L3_IPV4 (1ULL << 1)
#define BPF_F_ADJ_ROOM_ENCAP_L3_IPV6 (1ULL << 2)
#define BPF_F_ADJ_ROOM_ENCAP_L4_GRE (1ULL << 3)
#define BPF_F_ADJ_ROOM_ENCAP_L4_UDP (1ULL << 4)
#define BPF_F_ADJ_ROOM_ENCAP_L2(len) \
  (((__u64)len & BPF_ADJ_ROOM_ENCAP_L2_MASK) << BPF_ADJ_ROOM_ENCAP_L2_SHIFT)

/* BPF_FUNC_sysctl_get_name flags. */
#define BPF_F_SYSCTL_BASE_NAME (1ULL << 0)

/* BPF_FUNC_sk_storage_get flags */
#define BPF_SK_STORAGE_GET_F_CREATE (1ULL << 0)

/* Mode for BPF_FUNC_skb_adjust_room helper. */
enum bpf_adj_room_mode {
  BPF_ADJ_ROOM_NET,
  BPF_ADJ_ROOM_MAC,
};

/* Mode for BPF_FUNC_skb_load_bytes_relative helper. */
enum bpf_hdr_start_off {
  BPF_HDR_START_MAC,
  BPF_HDR_START_NET,
};

/* Encapsulation type for BPF_FUNC_lwt_push_encap helper. */
enum bpf_lwt_encap_mode {
  BPF_LWT_ENCAP_SEG6,
  BPF_LWT_ENCAP_SEG6_INLINE,
  BPF_LWT_ENCAP_IP,
};

#define __bpf_md_ptr(type, name) \
  union {                        \
    type name;                   \
    __u64 : 64;                  \
  } __attribute__((aligned(8)))

/* user accessible mirror of in-kernel sk_buff.
 * new fields can only be added to the end of this structure
 */
struct __sk_buff {
  __u32 len;
  __u32 pkt_type;
  __u32 mark;
  __u32 queue_mapping;
  __u32 protocol;
  __u32 vlan_present;
  __u32 vlan_tci;
  __u32 vlan_proto;
  __u32 priority;
  __u32 ingress_ifindex;
  __u32 ifindex;
  __u32 tc_index;
  __u32 cb[5];
  __u32 hash;
  __u32 tc_classid;
  __u32 data;
  __u32 data_end;
  __u32 napi_id;

  /* Accessed by BPF_PROG_TYPE_sk_skb types from here to ... */
  __u32 family;
  __u32 remote_ip4; /* Stored in network byte order */
  __u32 local_ip4; /* Stored in network byte order */
  __u32 remote_ip6[4]; /* Stored in network byte order */
  __u32 local_ip6[4]; /* Stored in network byte order */
  __u32 remote_port; /* Stored in network byte order */
  __u32 local_port; /* stored in host byte order */
  /* ... here. */

  __u32 data_meta;
  __bpf_md_ptr(struct bpf_flow_keys*, flow_keys);
  __u64 tstamp;
  __u32 wire_len;
  __u32 gso_segs;
  __bpf_md_ptr(struct bpf_sock*, sk);
};

struct bpf_tunnel_key {
  __u32 tunnel_id;
  union {
    __u32 remote_ipv4;
    __u32 remote_ipv6[4];
  };
  __u8 tunnel_tos;
  __u8 tunnel_ttl;
  __u16 tunnel_ext; /* Padding, future use. */
  __u32 tunnel_label;
};

/* user accessible mirror of in-kernel xfrm_state.
 * new fields can only be added to the end of this structure
 */
struct bpf_xfrm_state {
  __u32 reqid;
  __u32 spi; /* Stored in network byte order */
  __u16 family;
  __u16 ext; /* Padding, future use. */
  union {
    __u32 remote_ipv4; /* Stored in network byte order */
    __u32 remote_ipv6[4]; /* Stored in network byte order */
  };
};

/* Generic BPF return codes which all BPF program types may support.
 * The values are binary compatible with their TC_ACT_* counter-part to
 * provide backwards compatibility with existing SCHED_CLS and SCHED_ACT
 * programs.
 *
 * XDP is handled seprately, see XDP_*.
 */
enum bpf_ret_code {
  BPF_OK = 0,
  /* 1 reserved */
  BPF_DROP = 2,
  /* 3-6 reserved */
  BPF_REDIRECT = 7,
  /* >127 are reserved for prog type specific return codes.
   *
   * BPF_LWT_REROUTE: used by BPF_PROG_TYPE_LWT_IN and
   *    BPF_PROG_TYPE_LWT_XMIT to indicate that skb had been
   *    changed and should be routed based on its new L3 header.
   *    (This is an L3 redirect, as opposed to L2 redirect
   *    represented by BPF_REDIRECT above).
   */
  BPF_LWT_REROUTE = 128,
};

struct bpf_sock {
  __u32 bound_dev_if;
  __u32 family;
  __u32 type;
  __u32 protocol;
  __u32 mark;
  __u32 priority;
  /* IP address also allows 1 and 2 bytes access */
  __u32 src_ip4;
  __u32 src_ip6[4];
  __u32 src_port; /* host byte order */
  __u32 dst_port; /* network byte order */
  __u32 dst_ip4;
  __u32 dst_ip6[4];
  __u32 state;
};

struct bpf_tcp_sock {
  __u32 snd_cwnd; /* Sending congestion window    */
  __u32 srtt_us; /* smoothed round trip time << 3 in usecs */
  __u32 rtt_min;
  __u32 snd_ssthresh; /* Slow start size threshold    */
  __u32 rcv_nxt; /* What we want to receive next   */
  __u32 snd_nxt; /* Next sequence we send    */
  __u32 snd_una; /* First byte we want an ack for  */
  __u32 mss_cache; /* Cached effective mss, not including SACKS */
  __u32 ecn_flags; /* ECN status bits.     */
  __u32 rate_delivered; /* saved rate sample: packets delivered */
  __u32 rate_interval_us; /* saved rate sample: time elapsed */
  __u32 packets_out; /* Packets which are "in flight"  */
  __u32 retrans_out; /* Retransmitted packets out    */
  __u32 total_retrans; /* Total retransmits for entire connection */
  __u32 segs_in; /* RFC4898 tcpEStatsPerfSegsIn
                  * total number of segments in.
                  */
  __u32 data_segs_in; /* RFC4898 tcpEStatsPerfDataSegsIn
                       * total number of data segments in.
                       */
  __u32 segs_out; /* RFC4898 tcpEStatsPerfSegsOut
                   * The total number of segments sent.
                   */
  __u32 data_segs_out; /* RFC4898 tcpEStatsPerfDataSegsOut
                        * total number of data segments sent.
                        */
  __u32 lost_out; /* Lost packets     */
  __u32 sacked_out; /* SACK'd packets     */
  __u64 bytes_received; /* RFC4898 tcpEStatsAppHCThruOctetsReceived
                         * sum(delta(rcv_nxt)), or how many bytes
                         * were acked.
                         */
  __u64 bytes_acked; /* RFC4898 tcpEStatsAppHCThruOctetsAcked
                      * sum(delta(snd_una)), or how many bytes
                      * were acked.
                      */
  __u32 dsack_dups; /* RFC4898 tcpEStatsStackDSACKDups
                     * total number of DSACK blocks received
                     */
  __u32 delivered; /* Total data packets delivered incl. rexmits */
  __u32 delivered_ce; /* Like the above but only ECE marked packets */
  __u32 icsk_retransmits; /* Number of unrecovered [RTO] timeouts */
};

struct bpf_sock_tuple {
  union {
    struct {
      __be32 saddr;
      __be32 daddr;
      __be16 sport;
      __be16 dport;
    } ipv4;
    struct {
      __be32 saddr[4];
      __be32 daddr[4];
      __be16 sport;
      __be16 dport;
    } ipv6;
  };
};

struct bpf_xdp_sock {
  __u32 queue_id;
};

#define XDP_PACKET_HEADROOM 256

/* User return codes for XDP prog type.
 * A valid XDP program must return one of these defined values. All other
 * return codes are reserved for future use. Unknown return codes will
 * result in packet drops and a warning via bpf_warn_invalid_xdp_action().
 */
enum xdp_action {
  XDP_ABORTED = 0,
  XDP_DROP,
  XDP_PASS,
  XDP_TX,
  XDP_REDIRECT,
};

/* user accessible metadata for XDP packet hook
 * new fields must be added to the end of this structure
 */
struct xdp_md {
  __u32 data;
  __u32 data_end;
  __u32 data_meta;
  /* Below access go through struct xdp_rxq_info */
  __u32 ingress_ifindex; /* rxq->dev->ifindex */
  __u32 rx_queue_index; /* rxq->queue_index  */
};

enum sk_action {
  SK_DROP = 0,
  SK_PASS,
};

/* user accessible metadata for SK_MSG packet hook, new fields must
 * be added to the end of this structure
 */
struct sk_msg_md {
  __bpf_md_ptr(void*, data);
  __bpf_md_ptr(void*, data_end);

  __u32 family;
  __u32 remote_ip4; /* Stored in network byte order */
  __u32 local_ip4; /* Stored in network byte order */
  __u32 remote_ip6[4]; /* Stored in network byte order */
  __u32 local_ip6[4]; /* Stored in network byte order */
  __u32 remote_port; /* Stored in network byte order */
  __u32 local_port; /* stored in host byte order */
  __u32 size; /* Total size of sk_msg */
};

struct sk_reuseport_md {
  /*
   * Start of directly accessible data. It begins from
   * the tcp/udp header.
   */
  __bpf_md_ptr(void*, data);
  /* End of directly accessible data */
  __bpf_md_ptr(void*, data_end);
  /*
   * Total length of packet (starting from the tcp/udp header).
   * Note that the directly accessible bytes (data_end - data)
   * could be less than this "len".  Those bytes could be
   * indirectly read by a helper "bpf_skb_load_bytes()".
   */
  __u32 len;
  /*
   * Eth protocol in the mac header (network byte order). e.g.
   * ETH_P_IP(0x0800) and ETH_P_IPV6(0x86DD)
   */
  __u32 eth_protocol;
  __u32 ip_protocol; /* IP protocol. e.g. IPPROTO_TCP, IPPROTO_UDP */
  __u32 bind_inany; /* Is sock bound to an INANY address? */
  __u32 hash; /* A hash of the packet 4 tuples */
};

#define BPF_TAG_SIZE 8

struct bpf_prog_info {
  __u32 type;
  __u32 id;
  __u8 tag[BPF_TAG_SIZE];
  __u32 jited_prog_len;
  __u32 xlated_prog_len;
  __aligned_u64 jited_prog_insns;
  __aligned_u64 xlated_prog_insns;
  __u64 load_time; /* ns since boottime */
  __u32 created_by_uid;
  __u32 nr_map_ids;
  __aligned_u64 map_ids;
  char name[BPF_OBJ_NAME_LEN];
  __u32 ifindex;
  __u32 gpl_compatible : 1;
  __u32 : 31; /* alignment pad */
  __u64 netns_dev;
  __u64 netns_ino;
  __u32 nr_jited_ksyms;
  __u32 nr_jited_func_lens;
  __aligned_u64 jited_ksyms;
  __aligned_u64 jited_func_lens;
  __u32 btf_id;
  __u32 func_info_rec_size;
  __aligned_u64 func_info;
  __u32 nr_func_info;
  __u32 nr_line_info;
  __aligned_u64 line_info;
  __aligned_u64 jited_line_info;
  __u32 nr_jited_line_info;
  __u32 line_info_rec_size;
  __u32 jited_line_info_rec_size;
  __u32 nr_prog_tags;
  __aligned_u64 prog_tags;
  __u64 run_time_ns;
  __u64 run_cnt;
} __attribute__((aligned(8)));

struct bpf_map_info {
  __u32 type;
  __u32 id;
  __u32 key_size;
  __u32 value_size;
  __u32 max_entries;
  __u32 map_flags;
  char name[BPF_OBJ_NAME_LEN];
  __u32 ifindex;
  __u32 : 32;
  __u64 netns_dev;
  __u64 netns_ino;
  __u32 btf_id;
  __u32 btf_key_type_id;
  __u32 btf_value_type_id;
} __attribute__((aligned(8)));

struct bpf_btf_info {
  __aligned_u64 btf;
  __u32 btf_size;
  __u32 id;
} __attribute__((aligned(8)));

/* User bpf_sock_addr struct to access socket fields and sockaddr struct passed
 * by user and intended to be used by socket (e.g. to bind to, depends on
 * attach attach type).
 */
struct bpf_sock_addr {
  __u32 user_family; /* Allows 4-byte read, but no write. */
  __u32 user_ip4; /* Allows 1,2,4-byte read and 4-byte write.
                   * Stored in network byte order.
                   */
  __u32 user_ip6[4]; /* Allows 1,2,4,8-byte read and 4,8-byte write.
                      * Stored in network byte order.
                      */
  __u32 user_port; /* Allows 4-byte read and write.
                    * Stored in network byte order
                    */
  __u32 family; /* Allows 4-byte read, but no write */
  __u32 type; /* Allows 4-byte read, but no write */
  __u32 protocol; /* Allows 4-byte read, but no write */
  __u32 msg_src_ip4; /* Allows 1,2,4-byte read and 4-byte write.
                      * Stored in network byte order.
                      */
  __u32 msg_src_ip6[4]; /* Allows 1,2,4,8-byte read and 4,8-byte write.
                         * Stored in network byte order.
                         */
  __bpf_md_ptr(struct bpf_sock*, sk);
};

/* User bpf_sock_ops struct to access socket values and specify request ops
 * and their replies.
 * Some of this fields are in network (bigendian) byte order and may need
 * to be converted before use (bpf_ntohl() defined in samples/bpf/bpf_endian.h).
 * New fields can only be added at the end of this structure
 */
struct bpf_sock_ops {
  __u32 op;
  union {
    __u32 args[4]; /* Optionally passed to bpf program */
    __u32 reply; /* Returned by bpf program      */
    __u32 replylong[4]; /* Optionally returned by bpf prog  */
  };
  __u32 family;
  __u32 remote_ip4; /* Stored in network byte order */
  __u32 local_ip4; /* Stored in network byte order */
  __u32 remote_ip6[4]; /* Stored in network byte order */
  __u32 local_ip6[4]; /* Stored in network byte order */
  __u32 remote_port; /* Stored in network byte order */
  __u32 local_port; /* stored in host byte order */
  __u32 is_fullsock; /* Some TCP fields are only valid if
                      * there is a full socket. If not, the
                      * fields read as zero.
                      */
  __u32 snd_cwnd;
  __u32 srtt_us; /* Averaged RTT << 3 in usecs */
  __u32 bpf_sock_ops_cb_flags; /* flags defined in uapi/linux/tcp.h */
  __u32 state;
  __u32 rtt_min;
  __u32 snd_ssthresh;
  __u32 rcv_nxt;
  __u32 snd_nxt;
  __u32 snd_una;
  __u32 mss_cache;
  __u32 ecn_flags;
  __u32 rate_delivered;
  __u32 rate_interval_us;
  __u32 packets_out;
  __u32 retrans_out;
  __u32 total_retrans;
  __u32 segs_in;
  __u32 data_segs_in;
  __u32 segs_out;
  __u32 data_segs_out;
  __u32 lost_out;
  __u32 sacked_out;
  __u32 sk_txhash;
  __u64 bytes_received;
  __u64 bytes_acked;
  __bpf_md_ptr(struct bpf_sock*, sk);
};

/* Definitions for bpf_sock_ops_cb_flags */
#define BPF_SOCK_OPS_RTO_CB_FLAG (1 << 0)
#define BPF_SOCK_OPS_RETRANS_CB_FLAG (1 << 1)
#define BPF_SOCK_OPS_STATE_CB_FLAG (1 << 2)
#define BPF_SOCK_OPS_RTT_CB_FLAG (1 << 3)
#define BPF_SOCK_OPS_ALL_CB_FLAGS \
  0xF /* Mask of all currently    \
       * supported cb flags       \
       */

/* List of known BPF sock_ops operators.
 * New entries can only be added at the end
 */
enum {
  BPF_SOCK_OPS_VOID,
  BPF_SOCK_OPS_TIMEOUT_INIT, /* Should return SYN-RTO value to use or
                              * -1 if default value should be used
                              */
  BPF_SOCK_OPS_RWND_INIT, /* Should return initial advertized
                           * window (in packets) or -1 if default
                           * value should be used
                           */
  BPF_SOCK_OPS_TCP_CONNECT_CB, /* Calls BPF program right before an
                                * active connection is initialized
                                */
  BPF_SOCK_OPS_ACTIVE_ESTABLISHED_CB, /* Calls BPF program when an
                                       * active connection is
                                       * established
                                       */
  BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB, /* Calls BPF program when a
                                        * passive connection is
                                        * established
                                        */
  BPF_SOCK_OPS_NEEDS_ECN, /* If connection's congestion control
                           * needs ECN
                           */
  BPF_SOCK_OPS_BASE_RTT, /* Get base RTT. The correct value is
                          * based on the path and may be
                          * dependent on the congestion control
                          * algorithm. In general it indicates
                          * a congestion threshold. RTTs above
                          * this indicate congestion
                          */
  BPF_SOCK_OPS_RTO_CB, /* Called when an RTO has triggered.
                        * Arg1: value of icsk_retransmits
                        * Arg2: value of icsk_rto
                        * Arg3: whether RTO has expired
                        */
  BPF_SOCK_OPS_RETRANS_CB, /* Called when skb is retransmitted.
                            * Arg1: sequence number of 1st byte
                            * Arg2: # segments
                            * Arg3: return value of
                            *       tcp_transmit_skb (0 => success)
                            */
  BPF_SOCK_OPS_STATE_CB, /* Called when TCP changes state.
                          * Arg1: old_state
                          * Arg2: new_state
                          */
  BPF_SOCK_OPS_TCP_LISTEN_CB, /* Called on listen(2), right after
                               * socket transition to LISTEN state.
                               */
  BPF_SOCK_OPS_RTT_CB, /* Called on every RTT.
                        */
};

/* List of TCP states. There is a build check in net/ipv4/tcp.c to detect
 * changes between the TCP and BPF versions. Ideally this should never happen.
 * If it does, we need to add code to convert them before calling
 * the BPF sock_ops function.
 */
enum {
  BPF_TCP_ESTABLISHED = 1,
  BPF_TCP_SYN_SENT,
  BPF_TCP_SYN_RECV,
  BPF_TCP_FIN_WAIT1,
  BPF_TCP_FIN_WAIT2,
  BPF_TCP_TIME_WAIT,
  BPF_TCP_CLOSE,
  BPF_TCP_CLOSE_WAIT,
  BPF_TCP_LAST_ACK,
  BPF_TCP_LISTEN,
  BPF_TCP_CLOSING, /* Now a valid state */
  BPF_TCP_NEW_SYN_RECV,

  BPF_TCP_MAX_STATES /* Leave at the end! */
};

#define TCP_BPF_IW 1001 /* Set TCP initial congestion window */
#define TCP_BPF_SNDCWND_CLAMP 1002 /* Set sndcwnd_clamp */

struct bpf_perf_event_value {
  __u64 counter;
  __u64 enabled;
  __u64 running;
};

#define BPF_DEVCG_ACC_MKNOD (1ULL << 0)
#define BPF_DEVCG_ACC_READ (1ULL << 1)
#define BPF_DEVCG_ACC_WRITE (1ULL << 2)

#define BPF_DEVCG_DEV_BLOCK (1ULL << 0)
#define BPF_DEVCG_DEV_CHAR (1ULL << 1)

struct bpf_cgroup_dev_ctx {
  /* access_type encoded as (BPF_DEVCG_ACC_* << 16) | BPF_DEVCG_DEV_* */
  __u32 access_type;
  __u32 major;
  __u32 minor;
};

struct bpf_raw_tracepoint_args {
  __u64 args[0];
};

/* DIRECT:  Skip the FIB rules and go to FIB table associated with device
 * OUTPUT:  Do lookup from egress perspective; default is ingress
 */
#define BPF_FIB_LOOKUP_DIRECT (1U << 0)
#define BPF_FIB_LOOKUP_OUTPUT (1U << 1)

enum {
  BPF_FIB_LKUP_RET_SUCCESS, /* lookup successful */
  BPF_FIB_LKUP_RET_BLACKHOLE, /* dest is blackholed; can be dropped */
  BPF_FIB_LKUP_RET_UNREACHABLE, /* dest is unreachable; can be dropped */
  BPF_FIB_LKUP_RET_PROHIBIT, /* dest not allowed; can be dropped */
  BPF_FIB_LKUP_RET_NOT_FWDED, /* packet is not forwarded */
  BPF_FIB_LKUP_RET_FWD_DISABLED, /* fwding is not enabled on ingress */
  BPF_FIB_LKUP_RET_UNSUPP_LWT, /* fwd requires encapsulation */
  BPF_FIB_LKUP_RET_NO_NEIGH, /* no neighbor entry for nh */
  BPF_FIB_LKUP_RET_FRAG_NEEDED, /* fragmentation required to fwd */
};

struct bpf_fib_lookup {
  /* input:  network family for lookup (AF_INET, AF_INET6)
   * output: network family of egress nexthop
   */
  __u8 family;

  /* set if lookup is to consider L4 data - e.g., FIB rules */
  __u8 l4_protocol;
  __be16 sport;
  __be16 dport;

  /* total length of packet from network header - used for MTU check */
  __u16 tot_len;

  /* input: L3 device index for lookup
   * output: device index from FIB lookup
   */
  __u32 ifindex;

  union {
    /* inputs to lookup */
    __u8 tos; /* AF_INET  */
    __be32 flowinfo; /* AF_INET6, flow_label + priority */

    /* output: metric of fib result (IPv4/IPv6 only) */
    __u32 rt_metric;
  };

  union {
    __be32 ipv4_src;
    __u32 ipv6_src[4]; /* in6_addr; network order */
  };

  /* input to bpf_fib_lookup, ipv{4,6}_dst is destination address in
   * network header. output: bpf_fib_lookup sets to gateway address
   * if FIB lookup returns gateway route
   */
  union {
    __be32 ipv4_dst;
    __u32 ipv6_dst[4]; /* in6_addr; network order */
  };

  /* output */
  __be16 h_vlan_proto;
  __be16 h_vlan_TCI;
  __u8 smac[6]; /* ETH_ALEN */
  __u8 dmac[6]; /* ETH_ALEN */
};

enum bpf_task_fd_type {
  BPF_FD_TYPE_RAW_TRACEPOINT, /* tp name */
  BPF_FD_TYPE_TRACEPOINT, /* tp name */
  BPF_FD_TYPE_KPROBE, /* (symbol + offset) or addr */
  BPF_FD_TYPE_KRETPROBE, /* (symbol + offset) or addr */
  BPF_FD_TYPE_UPROBE, /* filename + offset */
  BPF_FD_TYPE_URETPROBE, /* filename + offset */
};

#define BPF_FLOW_DISSECTOR_F_PARSE_1ST_FRAG (1U << 0)
#define BPF_FLOW_DISSECTOR_F_STOP_AT_FLOW_LABEL (1U << 1)
#define BPF_FLOW_DISSECTOR_F_STOP_AT_ENCAP (1U << 2)

struct bpf_flow_keys {
  __u16 nhoff;
  __u16 thoff;
  __u16 addr_proto; /* ETH_P_* of valid addrs */
  __u8 is_frag;
  __u8 is_first_frag;
  __u8 is_encap;
  __u8 ip_proto;
  __be16 n_proto;
  __be16 sport;
  __be16 dport;
  union {
    struct {
      __be32 ipv4_src;
      __be32 ipv4_dst;
    };
    struct {
      __u32 ipv6_src[4]; /* in6_addr; network order */
      __u32 ipv6_dst[4]; /* in6_addr; network order */
    };
  };
  __u32 flags;
  __be32 flow_label;
};

struct bpf_func_info {
  __u32 insn_off;
  __u32 type_id;
};

#define BPF_LINE_INFO_LINE_NUM(line_col) ((line_col) >> 10)
#define BPF_LINE_INFO_LINE_COL(line_col) ((line_col) & 0x3ff)

struct bpf_line_info {
  __u32 insn_off;
  __u32 file_name_off;
  __u32 line_off;
  __u32 line_col;
};

struct bpf_spin_lock {
  __u32 val;
};

struct bpf_sysctl {
  __u32 write; /* Sysctl is being read (= 0) or written (= 1).
                * Allows 1,2,4-byte read, but no write.
                */
  __u32 file_pos; /* Sysctl file position to read from, write to.
                   * Allows 1,2,4-byte read an 4-byte write.
                   */
};

struct bpf_sockopt {
  __bpf_md_ptr(struct bpf_sock*, sk);
  __bpf_md_ptr(void*, optval);
  __bpf_md_ptr(void*, optval_end);

  __s32 level;
  __s32 optname;
  __s32 optlen;
  __s32 retval;
};

#endif /* __LINUX_BPF_H__ */
